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1 /**************************************************************************** |
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2 ** |
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3 ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). |
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38 ** $QT_END_LICENSE$ |
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39 ** |
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40 ****************************************************************************/ |
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41 |
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42 /*! |
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43 \page qt4-sql.html |
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44 \title The Qt 4 Database GUI Layer |
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45 |
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46 \contentspage {What's New in Qt 4}{Home} |
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47 \previouspage Cross-Platform Accessibility Support in Qt 4 |
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48 \nextpage The Network Module in Qt 4 |
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49 |
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50 The GUI layer of the SQL module in Qt 4 has been entirely |
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51 redesigned to work with \l{qt4-interview.html}{Interview} (Qt's |
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52 new model/view classes). It consists of three model classes |
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53 (QSqlQueryModel, QSqlTableModel, and QSqlRelationalTableModel) |
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54 that can be used with Qt's view classes, notably QTableView. |
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55 |
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56 \section1 General Overview |
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57 |
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58 The Qt 4 SQL classes are divided into three layers: |
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59 |
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60 \list |
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61 \o The database drivers |
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62 \o The core SQL classes |
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63 \o The GUI classes |
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64 \endlist |
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65 |
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66 The database drivers and the core SQL classes are mostly the same |
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67 as in Qt 3. The database item models are new with Qt 4; they |
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68 inherit from QAbstractItemModel and make it easy to present data |
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69 from a database in a view class such as QListView, QTableView, |
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70 and QTreeView. |
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71 |
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72 The philosophy behind the Qt 4 SQL module is that it should be |
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73 possible to use database models for rendering and editing data |
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74 just like any other item models. By changing the model at |
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75 run-time, you can decide whether you want to store your data in |
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76 an SQL database or in, say, an XML file. This generic approach |
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77 has the additional benefit that you don't need to know anything |
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78 about SQL to display and edit data. |
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79 |
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80 The Qt 4 SQL module includes three item models: |
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81 |
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82 \list |
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83 \o QSqlQueryModel is a read-only model based on an arbitrary |
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84 SQL query. |
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85 \o QSqlTableModel is a read-write model that works on a single |
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86 table. |
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87 \o QSqlRelationalTableModel is a QSqlTableModel subclass with |
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88 foreign key support. |
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89 \endlist |
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90 |
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91 Combined with Qt's view classes and Qt's default delegate class |
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92 (QItemDelegate), the models offer a very powerful mechanism for |
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93 accessing databases. For finer control on the rendering of the |
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94 fields, you can subclass one of the predefined models, or even |
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95 QAbstractItemDelegate or QItemDelegate if you need finer control. |
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96 |
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97 You can also perform some customizations without subclassing. For |
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98 example, you can sort a table using QSqlTableModel::sort(), and |
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99 you can initialize new rows by connecting to the |
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100 QSqlTableModel::primeInsert() signal. |
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101 |
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102 One nice feature supported by the read-write models is the |
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103 possibility to perform changes to the item model without |
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104 affecting the database until QSqlTableModel::submitAll() is |
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105 called. Changes can be dropped using QSqlTableModel::revertAll(). |
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106 |
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107 The new classes perform advantageously compared to the SQL |
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108 module's GUI layer in Qt 3. Speed and memory improvements in the |
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109 tool classes (especially QVariant, QString, and QMap) and in the |
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110 SQL drivers contribute to making Qt 4 database applications more |
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111 snappy. |
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112 |
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113 See the \l QtSql module overview for a more complete introduction |
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114 to Qt's SQL classes. |
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115 |
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116 \section1 Example Code |
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117 |
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118 The simplest way to present data from a database is to simply |
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119 combine a QSqlQueryModel with a QTableView: |
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120 |
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121 \snippet doc/src/snippets/code/doc_src_qt4-sql.qdoc 0 |
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122 |
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123 To present the contents of a single table, we can use |
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124 QSqlTableModel instead: |
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125 |
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126 \snippet doc/src/snippets/code/doc_src_qt4-sql.qdoc 1 |
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127 |
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128 In practice, it's common that we need to customize the rendering |
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129 of a field in the database. In that case, we can create our own |
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130 model based on QSqlQueryModel. The next code snippet shows a |
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131 custom model that prepends '#' to the value in field 0 and |
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132 converts the value in field 2 to uppercase: |
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133 |
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134 \snippet examples/sql/querymodel/customsqlmodel.h 0 |
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135 \codeline |
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136 \snippet examples/sql/querymodel/customsqlmodel.cpp 0 |
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137 |
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138 It is also possible to subclass QSqlQueryModel to add support for |
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139 editing. This is done by reimplementing |
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140 QAbstractItemModel::flags() to specify which database fields are |
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141 editable and QAbstractItemModel::setData() to modify the |
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142 database. Here's an example of a setData() reimplementation that |
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143 changes the first or last name of a person: |
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144 |
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145 \snippet examples/sql/querymodel/editablesqlmodel.cpp 1 |
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146 |
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147 It relies on helper functions called \c setFirstName() and |
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148 \c setLastName(), which execute an \c{update}. Here's |
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149 \c setFirstName(): |
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150 |
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151 \snippet examples/sql/querymodel/editablesqlmodel.cpp 2 |
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152 |
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153 See Qt's \c examples/sql directory for more examples. |
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154 |
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155 \section1 Comparison with Qt 3 |
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156 |
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157 The core SQL database classes haven't changed so much since Qt 3. |
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158 Here's a list of the main changes: |
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159 |
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160 \list |
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161 \o QSqlDatabase is now value-based instead of pointer-based. |
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162 \o QSqlFieldInfo and QSqlRecordInfo has been merged into |
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163 QSqlField and QSqlRecord. |
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164 \o The SQL query generation has been moved into the drivers. This |
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165 makes it possible to use non-standard SQL extensions. It also |
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166 opens the door to non-SQL databases. |
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167 \endlist |
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168 |
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169 The GUI-related database classes have been entirely redesigned. |
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170 The QSqlCursor abstraction has been replaced with QSqlQueryModel |
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171 and QSqlTableModel; QSqlEditorFactory is replaced by |
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172 QAbstractItemDelegate; QDataTable is replaced by QTableView. The |
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173 old classes are part of the \l{Qt3Support} library to aid |
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174 porting to Qt 4. |
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175 */ |