| author | Eckhart Koeppen <eckhart.koppen@nokia.com> |
| Wed, 28 Apr 2010 13:15:16 +0300 | |
| branch | RCL_3 |
| changeset 15 | b25b6dc3ff8b |
| parent 7 | 3f74d0d4af4c |
| permissions | -rw-r--r-- |
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/**************************************************************************** |
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** |
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** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). |
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** All rights reserved. |
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** Contact: Nokia Corporation (qt-info@nokia.com) |
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** |
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** This file is part of the documentation of the Qt Toolkit. |
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** |
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** $QT_BEGIN_LICENSE:LGPL$ |
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** No Commercial Usage |
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** This file contains pre-release code and may not be distributed. |
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** You may use this file in accordance with the terms and conditions |
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** contained in the Technology Preview License Agreement accompanying |
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** this package. |
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** |
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** GNU Lesser General Public License Usage |
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** Alternatively, this file may be used under the terms of the GNU Lesser |
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** General Public License version 2.1 as published by the Free Software |
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** Foundation and appearing in the file LICENSE.LGPL included in the |
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** packaging of this file. Please review the following information to |
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** ensure the GNU Lesser General Public License version 2.1 requirements |
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** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. |
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** |
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** In addition, as a special exception, Nokia gives you certain additional |
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** rights. These rights are described in the Nokia Qt LGPL Exception |
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** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. |
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** |
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** If you have questions regarding the use of this file, please contact |
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** Nokia at qt-info@nokia.com. |
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** |
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** |
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** |
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** |
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** |
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** |
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** |
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** |
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** $QT_END_LICENSE$ |
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** |
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****************************************************************************/ |
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/*! |
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\page xquery-introduction.html |
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\title A Short Path to XQuery |
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\startpage Using XML Technologies |
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\target XQuery-introduction |
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XQuery is a language for querying XML data or non-XML data that can be |
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modeled as XML. XQuery is specified by the \l{http://www.w3.org}{W3C}.
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\tableofcontents |
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\section1 Introduction |
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Where Java and C++ are \e{statement-based} languages, the XQuery
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language is \e{expression-based}. The simplest XQuery expression is an
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XML element constructor: |
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\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 20 |
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This \c{<recipe/>} element is an XQuery expression that forms a
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complete XQuery. In fact, this XQuery doesn't actually query |
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anything. It just creates an empty \c{<recipe/>} element in the
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output. But \l{Constructing Elements} {constructing new elements in an
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XQuery} is often necessary. |
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An XQuery expression can also be enclosed in curly braces and embedded |
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in another XQuery expression. This XQuery has a document expression |
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embedded in a node expression: |
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\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 21 |
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It creates a new \c{<html>} element in the output and sets its \c{id}
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attribute to be the \c{id} attribute from an \c{<html>} element in the
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\c{other.html} file.
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\section1 Using Path Expressions To Match & Select Items |
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In C++ and Java, we write nested \c{for} loops and recursive functions
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to traverse XML trees in search of elements of interest. In XQuery, we |
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write these iterative and recursive algorithms with \e{path
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expressions}. |
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A path expression looks somewhat like a typical \e{file pathname} for
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86 |
locating a file in a hierarchical file system. It is a sequence of one |
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87 |
or more \e{steps} separated by slash '/' or double slash '//'.
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Although path expressions are used for traversing XML trees, not file |
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89 |
systems, in QtXmlPatterms we can model a file system to look like an |
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XML tree, so in QtXmlPatterns we can use XQuery to traverse a file |
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91 |
system. See the \l {File System Example} {file system example}.
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92 |
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93 |
Think of a path expression as an algorithm for traversing an XML tree |
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94 |
to find and collect items of interest. This algorithm is evaluated by |
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95 |
evaluating each step moving from left to right through the sequence. A |
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step is evaluated with a set of input items (nodes and atomic values), |
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sometimes called the \e focus. The step is evaluated for each item in |
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the focus. These evaluations produce a new set of items, called the \e |
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99 |
result, which then becomes the focus that is passed to the next step. |
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Evaluation of the final step produces the final result, which is the |
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result of the XQuery. The items in the result set are presented in |
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\l{http://www.w3.org/TR/xquery/#id-document-order} {document order}
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and without duplicates. |
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104 |
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105 |
With QtXmlPatterns, a standard way to present the initial focus to a |
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query is to call QXmlQuery::setFocus(). Another common way is to let |
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the XQuery itself create the initial focus by using the first step of |
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108 |
the path expression to call the XQuery \c{doc()} function. The
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\c{doc()} function loads an XML document and returns the \e {document
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node}. Note that the document node is \e{not} the same as the
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\e{document element}. The \e{document node} is a node constructed in
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memory, when the document is loaded. It represents the entire XML |
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document, not the document element. The \e{document element} is the
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114 |
single, top-level XML element in the file. The \c{doc()} function
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115 |
returns the document node, which becomes the singleton node in the |
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116 |
initial focus set. The document node will have one child node, and |
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that child node will represent the document element. Consider the |
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118 |
following XQuery: |
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119 |
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\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 18 |
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121 |
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122 |
The \c{doc()} function loads the \c{cookbook.xml} file and returns the
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document node. The document node then becomes the focus for the next |
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step \c{//recipe}. Here the double slash means select all \c{<recipe>}
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125 |
elements found below the document node, regardless of where they |
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126 |
appear in the document tree. The query selects all \c{<recipe>}
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elements in the cookbook. See \l{Running The Cookbook Examples} for
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128 |
instructions on how to run this query (and most of the ones that |
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129 |
follow) from the command line. |
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130 |
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131 |
Conceptually, evaluation of the steps of a path expression is similar |
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132 |
to iterating through the same number of nested \e{for} loops. Consider
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133 |
the following XQuery, which builds on the previous one: |
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134 |
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135 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 19 |
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136 |
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137 |
This XQuery is a single path expression composed of three steps. The |
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138 |
first step creates the initial focus by calling the \c{doc()}
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139 |
function. We can paraphrase what the query engine does at each step: |
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140 |
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141 |
\list 1 |
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142 |
\o for each node in the initial focus (the document node)... |
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143 |
\o for each descendant node that is a \c{<recipe>} element...
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144 |
\o collect the child nodes that are \c{<title>} elements.
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145 |
\endlist |
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146 |
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147 |
Again the double slash means select all the \c{<recipe>} elements in the
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148 |
document. The single slash before the \c{<title>} element means select
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149 |
only those \c{<title>} elements that are \e{child} elements of a
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150 |
\c{<recipe>} element (i.e. not grandchildren, etc). The XQuery evaluates
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151 |
to a final result set containing the \c{<title>} element of each
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152 |
\c{<recipe>} element in the cookbook.
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153 |
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154 |
\section2 Axis Steps |
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155 |
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156 |
The most common kind of path step is called an \e{axis step}, which
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157 |
tells the query engine which way to navigate from the context node, |
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158 |
and which test to perform when it encounters nodes along the way. An |
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159 |
axis step has two parts, an \e{axis specifier}, and a \e{node test}.
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160 |
Conceptually, evaluation of an axis step proceeds as follows: For each |
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161 |
node in the focus set, the query engine navigates out from the node |
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162 |
along the specified axis and applies the node test to each node it |
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163 |
encounters. The nodes selected by the node test are collected in the |
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164 |
result set, which becomes the focus set for the next step. |
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165 |
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166 |
In the example XQuery above, the second and third steps are both axis |
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167 |
steps. Both apply the \c{element(name)} node test to nodes encountered
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while traversing along some axis. But in this example, the two axis |
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steps are written in a \l{Shorthand Form} {shorthand form}, where the
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axis specifier and the node test are not written explicitly but are |
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implied. XQueries are normally written in this shorthand form, but |
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they can also be written in the longhand form. If we rewrite the |
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XQuery in the longhand form, it looks like this: |
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174 |
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\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 22 |
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176 |
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The two axis steps have been expanded. The first step (\c{//recipe})
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has been rewritten as \c{/descendant-or-self::element(recipe)}, where
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\c{descendant-or-self::} is the axis specifier and \c{element(recipe)}
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is the node test. The second step (\c{title}) has been rewritten as
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\c{/child::element(title)}, where \c{child::} is the axis specifier
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and \c{element(title)} is the node test. The output of the expanded
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XQuery will be exactly the same as the output of the shorthand form. |
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184 |
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185 |
To create an axis step, concatenate an axis specifier and a node |
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186 |
test. The following sections list the axis specifiers and node tests |
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187 |
that are available. |
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188 |
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189 |
\section2 Axis Specifiers |
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190 |
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191 |
An axis specifier defines the direction you want the query engine to |
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192 |
take, when it navigates away from the context node. QtXmlPatterns |
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193 |
supports the following axes. |
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194 |
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195 |
\table |
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196 |
\header |
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197 |
\o Axis Specifier |
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\o refers to the axis containing... |
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199 |
\row |
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200 |
\o \c{self::}
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201 |
\o the context node itself |
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202 |
\row |
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\o \c{attribute::}
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\o all attribute nodes of the context node |
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\row |
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\o \c{child::}
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\o all child nodes of the context node (not attributes) |
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208 |
\row |
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\o \c{descendant::}
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\o all descendants of the context node (children, grandchildren, etc) |
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211 |
\row |
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212 |
\o \c{descendant-or-self::}
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\o all nodes in \c{descendant} + \c{self}
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\row |
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\o \c{parent::}
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\o the parent node of the context node, or empty if there is no parent |
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217 |
\row |
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\o \c{ancestor::}
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219 |
\o all ancestors of the context node (parent, grandparent, etc) |
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220 |
\row |
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221 |
\o \c{ancestor-or-self::}
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222 |
\o all nodes in \c{ancestor} + \c{self}
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223 |
\row |
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224 |
\o \c{following::}
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225 |
\o all nodes in the tree containing the context node, \e not |
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226 |
including \c{descendant}, \e and that follow the context node
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227 |
in the document |
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228 |
\row |
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229 |
\o \c{preceding::}
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230 |
\o all nodes in the tree contianing the context node, \e not |
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231 |
including \c{ancestor}, \e and that precede the context node in
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232 |
the document |
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233 |
\row |
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234 |
\o \c{following-sibling::}
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\o all children of the context node's \c{parent} that follow the
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236 |
context node in the document |
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237 |
\row |
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238 |
\o \c{preceding-sibling::}
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239 |
\o all children of the context node's \c{parent} that precede the
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240 |
context node in the document |
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241 |
\endtable |
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242 |
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243 |
\section2 Node Tests |
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244 |
|
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245 |
A node test is a conditional expression that must be true for a node |
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246 |
if the node is to be selected by the axis step. The conditional |
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expression can test just the \e kind of node, or it can test the \e |
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kind of node and the \e name of the node. The XQuery specification for |
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\l{http://www.w3.org/TR/xquery/#node-tests} {node tests} also defines
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250 |
a third condition, the node's \e {Schema Type}, but schema type tests
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251 |
are not supported in QtXmlPatterns. |
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QtXmlPatterns supports the following node tests. The tests that have a |
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\c{name} parameter test the node's name in addition to its \e{kind}
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and are often called the \l{Name Tests}.
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\table |
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\header |
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\o Node Test |
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\o matches all... |
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\row |
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\o \c{node()}
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\o nodes of any kind |
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\row |
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\o \c{text()}
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\o text nodes |
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\row |
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\o \c{comment()}
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\o comment nodes |
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\row |
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\o \c{element()}
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\o element nodes (same as star: *) |
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\row |
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\o \c{element(name)}
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\o element nodes named \c{name}
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\row |
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\o \c{attribute()}
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\o attribute nodes |
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\row |
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\o \c{attribute(name)}
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\o attribute nodes named \c{name}
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\row |
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\o \c{processing-instruction()}
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\o processing-instructions |
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\row |
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\o \c{processing-instruction(name)}
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\o processing-instructions named \c{name}
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\row |
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\o \c{document-node()}
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\o document nodes (there is only one) |
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\row |
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\o \c{document-node(element(name))}
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\o document node with document element \c{name}
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\endtable |
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295 |
|
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\target Shorthand Form |
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\section2 Shorthand Form |
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298 |
|
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Writing axis steps using the longhand form with axis specifiers and |
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node tests is semantically clear but syntactically verbose. The |
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shorthand form is easy to learn and, once you learn it, just as easy |
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to read. In the shorthand form, the axis specifier and node test are |
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implied by the syntax. XQueries are normally written in the shorthand |
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form. Here is a table of some frequently used shorthand forms: |
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305 |
|
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\table |
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\header |
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\o Shorthand syntax |
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\o Short for... |
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\o matches all... |
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\row |
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\o \c{name}
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\o \c{child::element(name)}
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\o child nodes that are \c{name} elements
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315 |
|
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\row |
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\o \c{*}
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\o \c{child::element()}
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\o child nodes that are elements (\c{node()} matches
|
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\e all child nodes) |
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321 |
|
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\row |
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\o \c{..}
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\o \c{parent::node()}
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\o parent nodes (there is only one) |
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326 |
|
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\row |
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\o \c{@*}
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\o \c{attribute::attribute()}
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\o attribute nodes |
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331 |
|
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\row |
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\o \c{@name}
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\o \c{attribute::attribute(name)}
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\o \c{name} attributes
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336 |
|
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\row |
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\o \c{//}
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\o \c{descendant-or-self::node()}
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340 |
\o descendent nodes (when used instead of '/') |
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341 |
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342 |
\endtable |
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343 |
|
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344 |
The \l{http://www.w3.org/TR/xquery/}{XQuery language specification}
|
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345 |
has a more detailed section on the shorthand form, which it calls the |
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346 |
\l{http://www.w3.org/TR/xquery/#abbrev} {abbreviated syntax}. More
|
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347 |
examples of path expressions written in the shorthand form are found |
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348 |
there. There is also a section listing examples of path expressions |
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349 |
written in the \l{http://www.w3.org/TR/xquery/#unabbrev} {longhand
|
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350 |
form}. |
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351 |
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352 |
\target Name Tests |
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353 |
\section2 Name Tests |
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354 |
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355 |
The name tests are the \l{Node Tests} that have the \c{name}
|
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356 |
parameter. A name test must match the node \e name in addition to the |
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357 |
node \e kind. We have already seen name tests used: |
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358 |
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359 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 19 |
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360 |
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361 |
In this path expression, both \c{recipe} and \c{title} are name tests
|
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362 |
written in the shorthand form. XQuery resolves these names |
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363 |
(\l{http://www.w3.org/TR/xquery/#id-basics}{QNames}) to their expanded
|
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364 |
form using whatever |
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365 |
\l{http://www.w3.org/TR/xquery/#dt-namespace-declaration} {namespace
|
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366 |
declarations} it knows about. Resolving a name to its expanded form |
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367 |
means replacing its namespace prefix, if one is present (there aren't |
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368 |
any present in the example), with a namespace URI. The expanded name |
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369 |
then consists of the namespace URI and the local name. |
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370 |
|
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371 |
But the names in the example above don't have namespace prefixes, |
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372 |
because we didn't include a namespace declaration in our |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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373 |
\c{cookbook.xml} file. However, we will often use XQuery to query XML
|
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374 |
documents that use namespaces. Forgetting to declare the correct |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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375 |
namespace(s) in an XQuery is a common cause of XQuery failures. Let's |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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376 |
add a \e{default} namespace to \c{cookbook.xml} now. Change the
|
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377 |
\e{document element} in \c{cookbook.xml} from:
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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378 |
|
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379 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 23 |
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380 |
|
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381 |
to... |
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382 |
|
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383 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 24 |
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|
384 |
|
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|
385 |
This is called a \e{default namespace} declaration because it doesn't
|
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|
386 |
include a namespace prefix. By including this default namespace |
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|
387 |
declaration in the document element, we mean that all unprefixed |
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|
388 |
\e{element} names in the document, including the document element
|
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|
389 |
itself (\c{cookbook}), are automatically in the default namespace
|
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|
390 |
\c{http://cookbook/namespace}. Note that unprefixed \e{attribute}
|
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|
391 |
names are not affected by the default namespace declaration. They are |
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|
392 |
always considered to be in \e{no namespace}. Note also that the URL
|
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|
393 |
we choose as our namespace URI need not refer to an actual location, |
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|
394 |
and doesn't refer to one in this case. But click on |
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|
395 |
\l{http://www.w3.org/XML/1998/namespace}, for example, which is the
|
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|
396 |
namespace URI for elements and attributes prefixed with \c{xml:}.
|
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|
397 |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
398 |
Now when we try to run the previous XQuery example, no output is |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
399 |
produced! The path expression no longer matches anything in the |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
400 |
cookbook file because our XQuery doesn't yet know about the namespace |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
401 |
declaration we added to the cookbook document. There are two ways we |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
402 |
can declare the namespace in the XQuery. We can give it a \e{namespace
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
403 |
prefix} (e.g. \c{c} for cookbook) and prefix each name test with the
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
404 |
namespace prefix: |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
405 |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
406 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 3 |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
407 |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
408 |
Or we can declare the namespace to be the \e{default element
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
409 |
namespace}, and then we can still run the original XQuery: |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
410 |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
411 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 4 |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
412 |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
413 |
Both methods will work and produce the same output, all the |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
414 |
\c{<title>} elements:
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
415 |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
416 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 5 |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
417 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
418 |
But note how the output is slightly different from the output we saw |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
419 |
before we added the default namespace declaration to the cookbook file. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
diff
changeset
|
420 |
QtXmlPatterns automatically includes the correct namespace attribute |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
diff
changeset
|
421 |
in each \c{<title>} element in the output. When QtXmlPatterns loads a
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
422 |
document and expands a QName, it creates an instance of QXmlName, |
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423 |
which retains the namespace prefix along with the namespace URI and |
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424 |
the local name. See QXmlName for further details. |
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|
425 |
|
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parents:
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|
426 |
One thing to keep in mind from this namespace discussion, whether you |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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|
427 |
run XQueries in a Qt program using QtXmlPatterns, or you run them from |
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|
428 |
the command line using xmlpatterns, is that if you don't get the |
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parents:
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|
429 |
output you expect, it might be because the data you are querying uses |
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|
430 |
namespaces, but you didn't declare those namespaces in your XQuery. |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
431 |
|
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|
432 |
\section3 Wildcards in Name Tests |
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changeset
|
433 |
|
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|
434 |
The wildcard \c{'*'} can be used in a name test. To find all the
|
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|
435 |
attributes in the cookbook but select only the ones in the \c{xml}
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
436 |
namespace, use the \c{xml:} namespace prefix but replace the
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
437 |
\e{local name} (the attribute name) with the wildcard:
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
438 |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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439 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 7 |
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changeset
|
440 |
|
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
441 |
Oops! If you save this XQuery in \c{file.xq} and run it through
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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|
442 |
\c{xmlpatterns}, it doesn't work. You get an error message instead,
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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|
443 |
something like this: \e{Error SENR0001 in file:///...file.xq, at line
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
444 |
1, column 1: Attribute xml:id can't be serialized because it appears |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
445 |
at the top level.} The XQuery actually ran correctly. It selected a |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
446 |
bunch of \c{xml:id} attributes and put them in the result set. But
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
447 |
then \c{xmlpatterns} sent the result set to a \l{QXmlSerializer}
|
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parents:
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changeset
|
448 |
{serializer}, which tried to output it as well-formed XML. Since the
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
449 |
result set contains only attributes and attributes alone are not |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
450 |
well-formed XML, the \l{QXmlSerializer} {serializer} reports a
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
451 |
\l{http://www.w3.org/TR/2005/WD-xslt-xquery-serialization-20050915/#id-errors}
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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|
452 |
{serialization error}.
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
453 |
|
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
454 |
Fear not. XQuery can do more than just find and select elements and |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
455 |
attributes. It can \l{Constructing Elements} {construct new ones on
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
456 |
the fly} as well, which is what we need to do here if we want |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
457 |
\c{xmlpatterns} to let us see the attributes we selected. The example
|
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
458 |
above and the ones below are revisited in the \l{Constructing
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
459 |
Elements} section. You can jump ahead to see the modified examples |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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|
460 |
now, and then come back, or you can press on from here. |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
461 |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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changeset
|
462 |
To find all the \c{name} attributes in the cookbook and select them
|
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
diff
changeset
|
463 |
all regardless of their namespace, replace the namespace prefix with |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
diff
changeset
|
464 |
the wildcard and write \c{name} (the attribute name) as the local
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
diff
changeset
|
465 |
name: |
|
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
466 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
diff
changeset
|
467 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 8 |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
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changeset
|
468 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
469 |
To find and select all the attributes of the \e{document element} in
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
470 |
the cookbook, replace the entire name test with the wildcard: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
471 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
472 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 9 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
473 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
474 |
\section1 Using Predicates In Path Expressions |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
475 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
476 |
Predicates can be used to further filter the nodes selected by a path |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
477 |
expression. A predicate is an expression in square brackets ('[' and
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
478 |
']') that either returns a boolean value or a number. A predicate can |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
diff
changeset
|
479 |
appear at the end of any path step in a path expression. The predicate |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
diff
changeset
|
480 |
is applied to each node in the focus set. If a node passes the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
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parents:
diff
changeset
|
481 |
filter, the node is included in the result set. The query below |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
482 |
selects the recipe element that has the \c{<title>} element
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
483 |
\c{"Hard-Boiled Eggs"}.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
484 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
485 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 10 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
486 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
487 |
The dot expression ('.') can be used in predicates and path
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
488 |
expressions to refer to the current context node. The following query |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
489 |
uses the dot expression to refer to the current \c{<method>} element.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
490 |
The query selects the empty \c{<method>} elements from the cookbook.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
491 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
492 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 11 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
493 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
494 |
Note that passing the dot expression to the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
495 |
\l{http://www.w3.org/TR/xpath-functions/#func-string-length}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
496 |
{string-length()} function is optional. When
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
497 |
\l{http://www.w3.org/TR/xpath-functions/#func-string-length}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
498 |
{string-length()} is called with no parameter, the context node is
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
499 |
assumed: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
500 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
501 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 12 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
502 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
503 |
Actually, selecting an empty \c{<method>} element might not be very
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
504 |
useful by itself. It doesn't tell you which recipe has the empty |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
505 |
method: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
506 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
507 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 31 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
508 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
509 |
\target Empty Method Not Robust |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
510 |
What you probably want to see instead are the \c{<recipe>} elements that
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
511 |
have empty \c{<method>} elements:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
512 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
513 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 32 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
514 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
515 |
The predicate uses the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
516 |
\l{http://www.w3.org/TR/xpath-functions/#func-string-length}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
517 |
{string-length()} function to test the length of each \c{<method>}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
518 |
element in each \c{<recipe>} element found by the node test. If a
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
519 |
\c{<method>} contains no text, the predicate evaluates to \c{true} and
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
520 |
the \c{<recipe>} element is selected. If the method contains some
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
521 |
text, the predicate evaluates to \c{false}, and the \c{<recipe>}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
522 |
element is discarded. The output is the entire recipe that has no |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
523 |
instructions for preparation: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
524 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
525 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 33 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
526 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
527 |
The astute reader will have noticed that this use of |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
528 |
\c{string-length()} to find an empty element is unreliable. It works
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
529 |
in this case, because the method element is written as \c{<method/>},
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
530 |
guaranteeing that its string length will be 0. It will still work if |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
531 |
the method element is written as \c{<method></method>}, but it will
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
532 |
fail if there is any whitespace between the opening and ending |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
533 |
\c{<method>} tags. A more robust way to find the recipes with empty
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
534 |
methods is presented in the section on \l{Boolean Predicates}.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
535 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
536 |
There are many more functions and operators defined for XQuery and |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
537 |
XPath. They are all \l{http://www.w3.org/TR/xpath-functions}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
538 |
{documented in the specification}.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
539 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
540 |
\section2 Positional Predicates |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
541 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
542 |
Predicates are often used to filter items based on their position in |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
543 |
a sequence. For path expressions processing items loaded from XML |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
544 |
documents, the normal sequence is |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
545 |
\l{http://www.w3.org/TR/xquery/#id-document-order} {document order}.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
546 |
This query returns the second \c{<recipe>} element in the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
547 |
\c{cookbook.xml} file:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
548 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
549 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 13 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
550 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
551 |
The other frequently used positional function is |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
552 |
\l{http://www.w3.org/TR/xpath-functions/#func-last} {last()}, which
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
553 |
returns the numeric position of the last item in the focus set. Stated |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
554 |
another way, \l{http://www.w3.org/TR/xpath-functions/#func-last}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
555 |
{last()} returns the size of the focus set. This query returns the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
556 |
last recipe in the cookbook: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
557 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
558 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 16 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
559 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
560 |
And this query returns the next to last \c{<recipe>}:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
561 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
562 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 17 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
563 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
564 |
\section2 Boolean Predicates |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
565 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
566 |
The other kind of predicate evaluates to \e true or \e false. A |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
567 |
boolean predicate takes the value of its expression and determines its |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
568 |
\e{effective boolean value} according to the following rules:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
569 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
570 |
\list |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
571 |
\o An expression that evaluates to a single node is \c{true}.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
572 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
573 |
\o An expression that evaluates to a string is \c{false} if the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
574 |
string is empty and \c{true} if the string is not empty.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
575 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
576 |
\o An expression that evaluates to a boolean value (i.e. type |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
577 |
\c{xs:boolean}) is that value.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
578 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
579 |
\o If the expression evaluates to anything else, it's an error |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
580 |
(e.g. type \c{xs:date}).
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
581 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
582 |
\endlist |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
583 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
584 |
We have already seen some boolean predicates in use. Earlier, we saw |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
585 |
a \e{not so robust} way to find the \l{Empty Method Not Robust}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
586 |
{recipes that have no instructions}. \c{[string-length(method) = 0]}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
587 |
is a boolean predicate that would fail in the example if the empty |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
588 |
method element was written with both opening and closing tags and |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
589 |
there was whitespace between the tags. Here is a more robust way that |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
590 |
uses a different boolean predicate. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
591 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
592 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 34 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
593 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
594 |
This one uses the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
595 |
\l{http://www.w3.org/TR/xpath-functions/#func-empty} {empty()} and
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
596 |
function to test whether the method contains any steps. If the method |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
597 |
contains no steps, then \c{empty(step)} will return \c{true}, and
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
598 |
hence the predicate will evaluate to \c{true}.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
599 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
600 |
But even that version isn't foolproof. Suppose the method does contain |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
601 |
steps, but all the steps themselves are empty. That's still a case of |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
602 |
a recipe with no instructions that won't be detected. There is a |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
603 |
better way: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
604 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
605 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 35 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
606 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
607 |
This version uses the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
608 |
\l{http://www.w3.org/TR/xpath-functions/#func-not} {not} and
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
609 |
\l{http://www.w3.org/TR/xpath-functions/#func-normalize-space}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
610 |
{normalize-space()} functions. \c{normalize-space(method))} returns
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
611 |
the contents of the method element as a string, but with all the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
612 |
whitespace normalized, i.e., the string value of each \c{<step>}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
613 |
element will have its whitespace normalized, and then all the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
614 |
normalized step values will be concatenated. If that string is empty, |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
615 |
then \c{not()} returns \c{true} and the predicate is \c{true}.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
616 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
617 |
We can also use the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
618 |
\l{http://www.w3.org/TR/xpath-functions/#func-position} {position()}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
619 |
function in a comparison to inspect positions with conditional logic. The |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
620 |
\l{http://www.w3.org/TR/xpath-functions/#func-position} {position()}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
621 |
function returns the position index of the current context item in the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
622 |
sequence of items: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
623 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
624 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 14 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
625 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
626 |
Note that the first position in the sequence is position 1, not 0. We |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
627 |
can also select \e{all} the recipes after the first one:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
628 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
629 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 15 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
630 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
631 |
\target Constructing Elements |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
632 |
\section1 Constructing Elements |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
633 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
634 |
In the section about \l{Wildcards in Name Tests} {using wildcards in
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
635 |
name tests}, we saw three simple example XQueries, each of which |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
636 |
selected a different list of XML attributes from the cookbook. We |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
637 |
couldn't use \c{xmlpatterns} to run these queries, however, because
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
638 |
\c{xmlpatterns} sends the XQuery results to a \l{QXmlSerializer}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
639 |
{serializer}, which expects to serialize the results as well-formed
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
640 |
XML. Since a list of XML attributes by itself is not well-formed XML, |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
641 |
the serializer reported an error for each XQuery. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
642 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
643 |
Since an attribute must appear in an element, for each attribute in |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
644 |
the result set, we must create an XML element. We can do that using a |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
645 |
\l{http://www.w3.org/TR/xquery/#id-for-let} {\e{for} clause} with a
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
646 |
\l{http://www.w3.org/TR/xquery/#id-variables} {bound variable}, and a
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
647 |
\l{http://www.w3.org/TR/xquery/#id-orderby-return} {\e{return}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
648 |
clause} with an element constructor: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
649 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
650 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 25 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
651 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
652 |
The \e{for} clause produces a sequence of attribute nodes from the result
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
653 |
of the path expression. Each attribute node in the sequence is bound |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
654 |
to the variable \c{$i}. The \e{return} clause then constructs a \c{<p>}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
655 |
element around the attribute node. Here is the output: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
656 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
657 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 28 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
658 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
659 |
The output contains one \c{<p>} element for each \c{xml:id} attribute
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
660 |
in the cookbook. Note that XQuery puts each attribute in the right |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
661 |
place in its \c{<p>} element, despite the fact that in the \e{return}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
662 |
clause, the \c{$i} variable is positioned as if it is meant to become
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
663 |
\c{<p>} element content.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
664 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
665 |
The other two examples from the \l{Wildcards in Name Tests} {wildcard}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
666 |
section can be rewritten the same way. Here is the XQuery that selects |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
667 |
all the \c{name} attributes, regardless of namespace:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
668 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
669 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 26 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
670 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
671 |
And here is its output: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
672 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
673 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 29 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
674 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
675 |
And here is the XQuery that selects all the attributes from the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
676 |
\e{document element}:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
677 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
678 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 27 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
679 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
680 |
And here is its output: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
681 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
682 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 30 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
683 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
684 |
\section2 Element Constructors are Expressions |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
685 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
686 |
Because node constructors are expressions, they can be used in |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
687 |
XQueries wherever expressions are allowed. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
688 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
689 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 40 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
690 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
691 |
If \c{cookbook.xml} is loaded without error, a \c{<oppskrift>} element
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
692 |
(Norwegian word for recipe) is constructed for each \c{<recipe>}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
693 |
element in the cookbook, and the child nodes of the \c{<recipe>} are
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
694 |
copied into the \c{<oppskrift>} element. But if the cookbook document
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
695 |
doesn't exist or does not contain well-formed XML, a single |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
696 |
\c{<oppskrift>} element is constructed containing an error message.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
697 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
698 |
\section1 Constructing Atomic Values |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
699 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
700 |
XQuery also has atomic values. An atomic value is a value in the value |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
701 |
space of one of the built-in datatypes in the \l |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
702 |
{http://www.w3.org/TR/xmlschema-2} {XML Schema language}. These
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
703 |
\e{atomic types} have built-in operators for doing arithmetic,
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
704 |
comparisons, and for converting values to other atomic types. See the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
705 |
\l {http://www.w3.org/TR/xmlschema-2/#built-in-datatypes} {Built-in
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
706 |
Datatype Hierarchy} for the entire tree of built-in, primitive and |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
707 |
derived atomic types. \note Click on a data type in the tree for its |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
708 |
detailed specification. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
709 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
710 |
To construct an atomic value as element content, enclose an expression |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
711 |
in curly braces and embed it in the element constructor: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
712 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
713 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 36 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
714 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
715 |
Sending this XQuery through xmlpatterns produces: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
716 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
717 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 37 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
718 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
719 |
To compute the value of an attribute, enclose the expression in |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
720 |
curly braces and embed it in the attribute value: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
721 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
722 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 38 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
723 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
724 |
Sending this XQuery through xmlpatterns produces: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
725 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
726 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 39 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
727 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
728 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 40 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
729 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
730 |
If \c{cookbook.xml} is loaded without error, a \c{<oppskrift>} element
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
731 |
(Norweigian word for recipe) is constructed for each \c{<recipe>}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
732 |
element in the cookbook, and the child nodes of the \c{<recipe>} are
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
733 |
copied into the \c{<oppskrift>} element. But if the cookbook document
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
734 |
doesn't exist or does not contain well-formed XML, a single |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
735 |
\c{<oppskrift>} element is constructed containing an error message.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
736 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
737 |
\section1 Running The Cookbook Examples |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
738 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
739 |
Most of the XQuery examples in this document refer to the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
740 |
\c{cookbook.xml} example file from the \l{Recipes Example}.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
741 |
Copy the \c{cookbook.xml} to your current directory, save one of the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
742 |
cookbook XQuery examples in a \c{.xq} file (e.g., \c{file.xq}), and
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
743 |
run the XQuery using Qt's command line utility: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
744 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
745 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 6 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
746 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
747 |
\section1 Further Reading |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
748 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
749 |
There is much more to the XQuery language than we have presented in |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
750 |
this short introduction. We will be adding more here in later |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
751 |
releases. In the meantime, playing with the \c{xmlpatterns} utility
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
752 |
and making modifications to the XQuery examples provided here will be |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
753 |
quite informative. An XQuery textbook will be a good investment. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
754 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
755 |
You can also ask questions on XQuery mail lists: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
756 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
757 |
\list |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
758 |
\o |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
759 |
\l{http://qt.nokia.com/lists/qt-interest/}{qt-interest}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
760 |
\o |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
761 |
\l{http://www.x-query.com/mailman/listinfo/talk}{talk at x-query.com}.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
762 |
\endlist |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
763 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
764 |
\l{http://www.functx.com/functx/}{FunctX} has a collection of XQuery
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
765 |
functions that can be both useful and educational. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
766 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
767 |
This introduction contains many links to the specifications, which, of course, |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
768 |
are the ultimate source of information about XQuery. They can be a bit |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
769 |
difficult, though, so consider investing in a textbook: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
770 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
771 |
\list |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
772 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
773 |
\o \l{http://www.w3.org/TR/xquery/}{XQuery 1.0: An XML Query
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
774 |
Language} - the main source for syntax and semantics. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
775 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
776 |
\o \l{http://www.w3.org/TR/xpath-functions/}{XQuery 1.0 and XPath
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
777 |
2.0 Functions and Operators} - the builtin functions and operators. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
778 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
779 |
\endlist |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
780 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
781 |
\section1 FAQ |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
782 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
783 |
The answers to these frequently asked questions explain the causes of |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
784 |
several common mistakes that most beginners make. Reading through the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
785 |
answers ahead of time might save you a lot of head scratching. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
786 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
787 |
\section2 Why didn't my path expression match anything? |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
788 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
789 |
The most common cause of this bug is failure to declare one or more |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
790 |
namespaces in your XQuery. Consider the following query for selecting |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
791 |
all the examples in an XHTML document: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
792 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
793 |
\quotefile snippets/patternist/simpleHTML.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
794 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
795 |
It won't match anything because \c{index.html} is an XHTML file, and
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
796 |
all XHTML files declare the default namespace |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
797 |
\c{"http://www.w3.org/1999/xhtml"} in their top (\c{<html>}) element.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
798 |
But the query doesn't declare this namespace, so the path expression |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
799 |
expands \c{html} to \c{{}html} and tries to match that expanded name.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
800 |
But the actual expanded name is |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
801 |
\c{{http://www.w3.org/1999/xhtml}html}. One possible fix is to declare the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
802 |
correct default namespace in the XQuery: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
803 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
804 |
\quotefile snippets/patternist/simpleXHTML.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
805 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
806 |
Another common cause of this bug is to confuse the \e{document node}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
807 |
with the top element node. They are different. This query won't match |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
808 |
anything: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
809 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
810 |
\quotefile snippets/patternist/docPlainHTML.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
811 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
812 |
The \c{doc()} function returns the \e{document node}, not the top
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
813 |
element node (\c{<html>}). Don't forget to match the top element node
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
814 |
in the path expression: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
815 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
816 |
\quotefile snippets/patternist/docPlainHTML2.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
817 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
818 |
\section2 What if my input namespace is different from my output namespace? |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
819 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
820 |
Just remember to declare both namespaces in your XQuery and use them |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
821 |
properly. Consider the following query, which is meant to generate |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
822 |
XHTML output from XML input: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
823 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
824 |
\quotefile snippets/patternist/embedDataInXHTML.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
825 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
826 |
We want the \c{<html>}, \c{<body>}, and \c{<p>} nodes we create in the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
827 |
output to be in the standard XHTML namespace, so we declare the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
828 |
default namespace to be \c{http://www.w3.org/1999/xhtml}. That's
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
829 |
correct for the output, but that same default namespace will also be |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
830 |
applied to the node names in the path expression we're trying to match |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
831 |
in the input (\c{/tests/test[@status = "failure"]}), which is wrong,
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
832 |
because the namespace used in \c{testResult.xml} is perhaps in the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
833 |
empty namespace. So we must declare that namespace too, with a |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
834 |
namespace prefix, and then use the prefix with the node names in |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
835 |
the path expression. This one will probably work better: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
836 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
837 |
\quotefile snippets/patternist/embedDataInXHTML2.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
838 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
839 |
\section2 Why doesn't my return clause work? |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
840 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
841 |
Recall that XQuery is an \e{expression-based} language, not
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
842 |
\e{statement-based}. Because an XQuery is a lot of expressions,
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
843 |
understanding XQuery expression precedence is very important. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
844 |
Consider the following query: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
845 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
846 |
\quotefile snippets/patternist/forClause2.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
847 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
848 |
It looks ok, but it isn't. It is supposed to be a FLWOR expression |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
849 |
comprising a \e{for} clause and a \e{return} clause, but it isn't just
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
850 |
that. It \e{has} a FLWOR expression, certainly (with the \e{for} and
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
851 |
\e{return} clauses), but it \e{also} has an arithmetic expression
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
852 |
(\e{+ $d}) dangling at the end because we didn't enclose the return
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
853 |
expression in parentheses. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
854 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
855 |
Using parentheses to establish precedence is more important in XQuery |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
856 |
than in other languages, because XQuery is \e{expression-based}. In
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
857 |
In this case, without parantheses enclosing \c{$i + $d}, the return
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
858 |
clause only returns \c{$i}. The \c{+$d} will have the result of the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
859 |
FLWOR expression as its left operand. And, since the scope of variable |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
860 |
\c{$d} ends at the end of the \e{return} clause, a variable out of
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
861 |
scope error will be reported. Correct these problems by using |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
862 |
parentheses. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
863 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
864 |
\quotefile snippets/patternist/forClause.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
865 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
866 |
\section2 Why didn't my expression get evaluated? |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
867 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
868 |
You probably misplaced some curly braces. When you want an expression |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
869 |
evaluated inside an element constructor, enclose the expression in |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
870 |
curly braces. Without the curly braces, the expression will be |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
871 |
interpreted as text. Here is a \c{sum()} expression used in an \c{<e>}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
872 |
element. The table shows cases where the curly braces are missing, |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
873 |
misplaced, and placed correctly: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
874 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
875 |
\table |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
876 |
\header |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
877 |
\o element constructor with expression... |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
878 |
\o evaluates to... |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
879 |
\row |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
880 |
\o <e>sum((1, 2, 3))</e> |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
881 |
\o <e>sum((1, 2, 3))</e> |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
882 |
\row |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
883 |
\o <e>sum({(1, 2, 3)})</e>
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
884 |
\o <e>sum(1 2 3)</e> |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
885 |
\row |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
886 |
\o <e>{sum((1, 2, 3))}</e>
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
887 |
\o <e>6</e> |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
888 |
\endtable |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
889 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
890 |
\section2 My predicate is correct, so why doesn't it select the right stuff? |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
891 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
892 |
Either you put your predicate in the wrong place in your path |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
893 |
expression, or you forgot to add some parentheses. Consider this |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
894 |
input file \c{doc.txt}:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
895 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
896 |
\quotefile snippets/patternist/doc.txt |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
897 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
898 |
Suppose you want the first \c{<span>} element of every \c{<p>}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
899 |
element. Apply a position filter (\c{[1]}) to the \c{/span} path step:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
900 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
901 |
\quotefile snippets/patternist/filterOnStep.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
902 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
903 |
Applying the \c{[1]} filter to the \c{/span} step returns the first
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
904 |
\c{<span>} element of each \c{<p>} element:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
905 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
906 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 41 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
907 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
908 |
\note: You can write the same query this way: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
909 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
910 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 44 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
911 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
912 |
Or you can reduce it right down to this: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
913 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
914 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 45 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
915 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
916 |
On the other hand, suppose you really want only one \c{<span>}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
917 |
element, the first one in the document (i.e., you only want the first |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
918 |
\c{<span>} element in the first \c{<p>} element). Then you have to do
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
919 |
more filtering. There are two ways you can do it. You can apply the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
920 |
\c{[1]} filter in the same place as above but enclose the path
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
921 |
expression in parentheses: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
922 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
923 |
\quotefile snippets/patternist/filterOnPath.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
924 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
925 |
Or you can apply a second position filter (\c{[1]} again) to the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
926 |
\c{/p} path step:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
927 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
928 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 43 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
929 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
930 |
Either way the query will return only the first \c{<span>} element in
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
931 |
the document: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
932 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
933 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 42 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
934 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
935 |
\section2 Why doesn't my FLWOR behave as expected? |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
936 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
937 |
The quick answer is you probably expected your XQuery FLWOR to behave |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
938 |
just like a C++ \e{for} loop. But they aren't the same. Consider a
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
939 |
simple example: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
940 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
941 |
\quotefile snippets/patternist/letOrderBy.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
942 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
943 |
This query evaluates to \e{4 -4 -2 2 -8 8}. The \e{for} clause does
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
944 |
set up a \e{for} loop style iteration, which does evaluate the rest of
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
945 |
the FLWOR multiple times, one time for each value returned by the |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
946 |
\e{in} expression. That much is similar to the C++ \e{for} loop.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
947 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
948 |
But consider the \e{return} clause. In C++ if you hit a \e{return}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
949 |
statement, you break out of the \e{for} loop and return from the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
950 |
function with one value. Not so in XQuery. The \e{return} clause is
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
951 |
the last clause of the FLWOR, and it means: \e{Append the return value
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
952 |
to the result list and then begin the next iteration of the FLWOR}. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
953 |
When the \e{for} clause's \e{in} expression no longer returns a value,
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
954 |
the entire result list is returned. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
955 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
956 |
Next, consider the \e{order by} clause. It doesn't do any sorting on
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
957 |
each iteration of the FLWOR. It just evaluates its expression on each |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
958 |
iteration (\c{$a} in this case) to get an ordering value to map to the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
959 |
result item from each iteration. These ordering values are kept in a |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
960 |
parallel list. The result list is sorted at the end using the parallel |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
961 |
list of ordering values. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
962 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
963 |
The last difference to note here is that the \e{let} clause does
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
964 |
\e{not} set up an iteration through a sequence of values like the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
965 |
\e{for} clause does. The \e{let} clause isn't a sort of nested loop.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
966 |
It isn't a loop at all. It is just a variable binding. On each |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
967 |
iteration, it binds the \e{entire} sequence of values on the right to
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
968 |
the variable on the left. In the example above, it binds (4 -4) to |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
969 |
\c{$b} on the first iteration, (-2 2) on the second iteration, and (-8
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
970 |
8) on the third iteration. So the following query doesn't iterate |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
971 |
through anything, and doesn't do any ordering: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
972 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
973 |
\quotefile snippets/patternist/invalidLetOrderBy.xq |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
974 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
975 |
It binds the entire sequence (2, 3, 1) to \c{$i} one time only; the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
976 |
\e{order by} clause only has one thing to order and hence does
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
977 |
nothing, and the query evaluates to 2 3 1, the sequence assigned to |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
978 |
\c{$i}.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
979 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
980 |
\note We didn't include a \e{where} clause in the example. The
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
981 |
\e{where} clause is for filtering results.
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
982 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
983 |
\section2 Why are my elements created in the wrong order? |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
984 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
985 |
The short answer is your elements are \e{not} created in the wrong
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
986 |
order, because when appearing as operands to a path expression, |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
987 |
there is no correct order. Consider the following query, |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
988 |
which again uses the input file \c{doc.txt}:
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
989 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
990 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 46 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
991 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
992 |
The query finds all the \c{<p>} elements in the file. For each \c{<p>}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
993 |
element, it builds a \c{<p>} element in the output containing the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
994 |
concatenated contents of all the \c{<p>} element's child \c{<span>}
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
995 |
elements. Running the query through \c{xmlpatterns} might produce the
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
996 |
following output, which is not sorted in the expected order. |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
997 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
998 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 47 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
999 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
1000 |
You can use a \e{for} loop to ensure that the order of
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
1001 |
the result set corresponds to the order of the input sequence: |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
1002 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
1003 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 48 |
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
|
1004 |
|
|
3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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1005 |
This version produces the same result set but in the expected order: |
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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changeset
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1006 |
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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changeset
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1007 |
\snippet snippets/code/doc_src_qtxmlpatterns.qdoc 49 |
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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changeset
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1008 |
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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changeset
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1009 |
\section2 Why can't I use \c{true} and \c{false} in my XQuery?
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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changeset
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1010 |
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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changeset
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1011 |
You can, but not by just using the names \c{true} and \c{false}
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qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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changeset
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1012 |
directly, because they are \l{Name Tests} {name tests} although they look
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
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1013 |
like boolean constants. The simple way to create the boolean values is |
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
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1014 |
to use the builtin functions \c{true()} and \c{false()} wherever
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
diff
changeset
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1015 |
you want to use \c{true} and \c{false}. The other way is to invoke the
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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changeset
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1016 |
boolean constructor: |
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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changeset
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1017 |
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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changeset
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1018 |
\quotefile snippets/patternist/xsBooleanTrue.xq |
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3f74d0d4af4c
qt:70947f0f93d948bc89b3b43d00da758a51f1ef84
Eckhart Koeppen <eckhart.koppen@nokia.com>
parents:
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changeset
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1019 |
*/ |