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+
+/*!
+ \example sql/sqlwidgetmapper
+ \title SQL Widget Mapper Example
+
+ The SQL Widget Mapper example shows how to use a map information from a
+ database to widgets on a form.
+
+ \image sql-widget-mapper.png
+
+ In the \l{Combo Widget Mapper Example}, we showed how to use a named
+ mapping between a widget mapper and a QComboBox widget with a special
+ purpose model to relate values in the model to a list of choices.
+
+ Again, we create a \c Window class with an almost identical user interface,
+ providing a combo box to allow their addresses to be classified as "Home",
+ "Work" or "Other". However, instead of using a separate model to hold these
+ address types, we use one database table to hold the example data and
+ another to hold the address types. In this way, we store all the
+ information in the same place.
+
+ \section1 Window Class Definition
+
+ The class provides a constructor, a slot to keep the buttons up to date,
+ and a private function to set up the model:
+
+ \snippet examples/sql/sqlwidgetmapper/window.h Window definition
+
+ In addition to the QDataWidgetMapper object and the controls used to make
+ up the user interface, we use a QStandardItemModel to hold our data and
+ a QStringListModel to hold information about the types of address that
+ can be applied to each person's data.
+
+ \section1 Window Class Implementation
+
+ The first act performed by the \c Window class constructor is to set up
+ the model used to hold the example data. Since this is a key part of the
+ example, we will look at this first.
+
+ The model is initialized in the window's \c{setupModel()} function. Here,
+ we create a SQLite database containing a "person" table with primary key,
+ name, address and type fields.
+
+ \snippet examples/sql/sqlwidgetmapper/window.cpp Set up the main table
+
+ On each row of the table, we insert default values for these fields,
+ including values for the address types that correspond to the address
+ types are stored in a separate table.
+
+ \image widgetmapper-sql-mapping-table.png
+
+ We create an "addresstype" table containing the identifiers used in the
+ "person" table and the corresponding strings:
+
+ \snippet examples/sql/sqlwidgetmapper/window.cpp Set up the address type table
+
+ The "typeid" field in the "person" table is related to the contents of
+ the "addresstype" table via a relation in a QSqlRelationalTableModel.
+ This kind of model performs all the necessary work to store the data in
+ a database and also allows any relations to be used as models in their
+ own right.
+
+ In this case, we have defined a relation for the "typeid" field in the
+ "person" table that relates it to the "id" field in the "addresstype"
+ table and which causes the contents of the "description" field to be
+ used wherever the "typeid" is presented to the user. (See the
+ QSqlRelationalTableModel::setRelation() documentation for details.)
+
+ \image widgetmapper-sql-mapping.png
+
+ The constructor of the \c Window class can be explained in three parts.
+ In the first part, we set up the model used to hold the data, then we set
+ up the widgets used for the user interface:
+
+ \snippet examples/sql/sqlwidgetmapper/window.cpp Set up widgets
+
+ We obtain a model for the combo box from the main model, based on the
+ relation we set up for the "typeid" field. The call to the combo box's
+ \l{QComboBox::}{setModelColumn()} selects the field in the field in the
+ model to display.
+
+ Note that this approach is similar to the one used in the
+ \l{Combo Widget Mapper Example} in that we set up a model for the
+ combo box. However, in this case, we obtain a model based on a relation
+ in the QSqlRelationalTableModel rather than create a separate one.
+
+ Next, we set up the widget mapper, relating each input widget to a field
+ in the model:
+
+ \snippet examples/sql/sqlwidgetmapper/window.cpp Set up the mapper
+
+ For the combo box, we already know the index of the field in the model
+ from the \c{setupModel()} function. We use a QSqlRelationalDelegate as
+ a proxy between the mapper and the input widgets to match up the "typeid"
+ values in the model with those in the combo box's model and populate the
+ combo box with descriptions rather than integer values.
+
+ As a result, the user is able to select an item from the combo box,
+ and the associated value is written back to the model.
+
+ The rest of the constructor is very similar to that of the
+ \l{Simple Widget Mapper Example}:
+
+ \snippet examples/sql/sqlwidgetmapper/window.cpp Set up connections and layouts
+
+ We show the implementation of the \c{updateButtons()} slot for
+ completeness:
+
+ \snippet examples/sql/sqlwidgetmapper/window.cpp Slot for updating the buttons
+
+ \omit
+ \section1 Delegate Class Definition and Implementation
+
+ The delegate we use to mediate interaction between the widget mapper and
+ the input widgets is a small QItemDelegate subclass:
+
+ \snippet examples/sql/sqlwidgetmapper/delegate.h Delegate class definition
+
+ This provides implementations of the two standard functions used to pass
+ data between editor widgets and the model (see the \l{Delegate Classes}
+ documentation for a more general description of these functions).
+
+ Since we only provide an empty implementation of the constructor, we
+ concentrate on the other two functions.
+
+ The \l{QItemDelegate::}{setEditorData()} implementation takes the data
+ referred to by the model index supplied and processes it according to
+ the presence of a \c currentIndex property in the editor widget:
+
+ \snippet examples/sql/sqlwidgetmapper/delegate.cpp setEditorData implementation
+
+ If, like QComboBox, the editor widget has this property, it is set using
+ the value from the model. Since we are passing around QVariant values,
+ the strings stored in the model are automatically converted to the integer
+ values needed for the \c currentIndex property.
+
+ As a result, instead of showing "0", "1" or "2" in the combo box, one of
+ its predefined set of items is shown. We call QItemDelegate::setEditorData()
+ for widgets without the \c currentIndex property.
+
+ The \l{QItemDelegate::}{setModelData()} implementation performs the reverse
+ process, taking the value stored in the widget's \c currentIndex property
+ and storing it back in the model:
+
+ \snippet examples/sql/sqlwidgetmapper/delegate.cpp setModelData implementation
+ \endomit
+
+ \section1 Summary and Further Reading
+
+ The use of a separate model for the combo box and a special delegate for the
+ widget mapper allows us to present a menu of choices to the user. Although
+ the choices are stored in the same database as the user's data, they are held
+ in a separate table. Using this approach, we can reconstructed complete records
+ at a later time while using database features appropriately.
+
+ If SQL models are not being used, it is still possible to use more than
+ one model to present choices to the user. This is covered by the
+ \l{Combo Widget Mapper Example}.
+*/