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    41 

    42 /*!

    43     \example sql/sqlwidgetmapper

    44     \title SQL Widget Mapper Example

    45 

    46     The SQL Widget Mapper example shows how to use a map information from a

    47     database to widgets on a form.

    48 

    49     \image sql-widget-mapper.png

    50 

    51     In the \l{Combo Widget Mapper Example}, we showed how to use a named

    52     mapping between a widget mapper and a QComboBox widget with a special

    53     purpose model to relate values in the model to a list of choices.

    54 

    55     Again, we create a \c Window class with an almost identical user interface,

    56     providing a combo box to allow their addresses to be classified as "Home",

    57     "Work" or "Other". However, instead of using a separate model to hold these

    58     address types, we use one database table to hold the example data and

    59     another to hold the address types. In this way, we store all the

    60     information in the same place.

    61 

    62     \section1 Window Class Definition

    63 

    64     The class provides a constructor, a slot to keep the buttons up to date,

    65     and a private function to set up the model:

    66 

    67     \snippet examples/sql/sqlwidgetmapper/window.h Window definition

    68 

    69     In addition to the QDataWidgetMapper object and the controls used to make

    70     up the user interface, we use a QStandardItemModel to hold our data and

    71     a QStringListModel to hold information about the types of address that

    72     can be applied to each person's data.

    73 

    74     \section1 Window Class Implementation

    75 

    76     The first act performed by the \c Window class constructor is to set up

    77     the model used to hold the example data. Since this is a key part of the

    78     example, we will look at this first.

    79 

    80     The model is initialized in the window's \c{setupModel()} function. Here,

    81     we create a SQLite database containing a "person" table with primary key,

    82     name, address and type fields.

    83 

    84     \snippet examples/sql/sqlwidgetmapper/window.cpp Set up the main table

    85 

    86     On each row of the table, we insert default values for these fields,

    87     including values for the address types that correspond to the address

    88     types are stored in a separate table.

    89 

    90     \image widgetmapper-sql-mapping-table.png

    91 

    92     We create an "addresstype" table containing the identifiers used in the

    93     "person" table and the corresponding strings:

    94 

    95     \snippet examples/sql/sqlwidgetmapper/window.cpp Set up the address type table

    96 

    97     The "typeid" field in the "person" table is related to the contents of

    98     the "addresstype" table via a relation in a QSqlRelationalTableModel.

    99     This kind of model performs all the necessary work to store the data in

   100     a database and also allows any relations to be used as models in their

   101     own right.

   102 

   103     In this case, we have defined a relation for the "typeid" field in the

   104     "person" table that relates it to the "id" field in the "addresstype"

   105     table and which causes the contents of the "description" field to be

   106     used wherever the "typeid" is presented to the user. (See the

   107     QSqlRelationalTableModel::setRelation() documentation for details.)

   108 

   109     \image widgetmapper-sql-mapping.png

   110 

   111     The constructor of the \c Window class can be explained in three parts.

   112     In the first part, we set up the model used to hold the data, then we set

   113     up the widgets used for the user interface:

   114 

   115     \snippet examples/sql/sqlwidgetmapper/window.cpp Set up widgets

   116 

   117     We obtain a model for the combo box from the main model, based on the

   118     relation we set up for the "typeid" field. The call to the combo box's

   119     \l{QComboBox::}{setModelColumn()} selects the field in the field in the

   120     model to display.

   121 

   122     Note that this approach is similar to the one used in the

   123     \l{Combo Widget Mapper Example} in that we set up a model for the

   124     combo box. However, in this case, we obtain a model based on a relation

   125     in the QSqlRelationalTableModel rather than create a separate one.

   126 

   127     Next, we set up the widget mapper, relating each input widget to a field

   128     in the model:

   129 

   130     \snippet examples/sql/sqlwidgetmapper/window.cpp Set up the mapper

   131 

   132     For the combo box, we already know the index of the field in the model

   133     from the \c{setupModel()} function. We use a QSqlRelationalDelegate as

   134     a proxy between the mapper and the input widgets to match up the "typeid"

   135     values in the model with those in the combo box's model and populate the

   136     combo box with descriptions rather than integer values.

   137 

   138     As a result, the user is able to select an item from the combo box,

   139     and the associated value is written back to the model.

   140 

   141     The rest of the constructor is very similar to that of the

   142     \l{Simple Widget Mapper Example}:

   143 

   144     \snippet examples/sql/sqlwidgetmapper/window.cpp Set up connections and layouts

   145 

   146     We show the implementation of the \c{updateButtons()} slot for

   147     completeness:

   148 

   149     \snippet examples/sql/sqlwidgetmapper/window.cpp Slot for updating the buttons

   150 

   151     \omit

   152     \section1 Delegate Class Definition and Implementation

   153 

   154     The delegate we use to mediate interaction between the widget mapper and

   155     the input widgets is a small QItemDelegate subclass:

   156 

   157     \snippet examples/sql/sqlwidgetmapper/delegate.h Delegate class definition

   158 

   159     This provides implementations of the two standard functions used to pass

   160     data between editor widgets and the model (see the \l{Delegate Classes}

   161     documentation for a more general description of these functions).

   162 

   163     Since we only provide an empty implementation of the constructor, we

   164     concentrate on the other two functions.

   165 

   166     The \l{QItemDelegate::}{setEditorData()} implementation takes the data

   167     referred to by the model index supplied and processes it according to

   168     the presence of a \c currentIndex property in the editor widget:

   169 

   170     \snippet examples/sql/sqlwidgetmapper/delegate.cpp setEditorData implementation

   171 

   172     If, like QComboBox, the editor widget has this property, it is set using

   173     the value from the model. Since we are passing around QVariant values,

   174     the strings stored in the model are automatically converted to the integer

   175     values needed for the \c currentIndex property.

   176 

   177     As a result, instead of showing "0", "1" or "2" in the combo box, one of

   178     its predefined set of items is shown. We call QItemDelegate::setEditorData()

   179     for widgets without the \c currentIndex property.

   180 

   181     The \l{QItemDelegate::}{setModelData()} implementation performs the reverse

   182     process, taking the value stored in the widget's \c currentIndex property

   183     and storing it back in the model:

   184 

   185     \snippet examples/sql/sqlwidgetmapper/delegate.cpp setModelData implementation

   186     \endomit

   187 

   188     \section1 Summary and Further Reading

   189 

   190     The use of a separate model for the combo box and a special delegate for the

   191     widget mapper allows us to present a menu of choices to the user. Although

   192     the choices are stored in the same database as the user's data, they are held

   193     in a separate table. Using this approach, we can reconstructed complete records

   194     at a later time while using database features appropriately.

   195 

   196     If SQL models are not being used, it is still possible to use more than

   197     one model to present choices to the user. This is covered by the

   198     \l{Combo Widget Mapper Example}.

   199 */