source: trunk/doc/src/examples/sqlwidgetmapper.qdoc@ 560

/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Qt Software Information ([email protected])
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial Usage
** Licensees holding valid Qt Commercial licenses may use this file in
** accordance with the Qt Commercial License Agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Nokia.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain
** additional rights. These rights are described in the Nokia Qt LGPL
** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this
** package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
** If you are unsure which license is appropriate for your use, please
** contact the sales department at [email protected].
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \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