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# QSqlRelationalTableModel Class Reference

The QSqlRelationalTableModel class provides an editable data model for a single database table, with foreign key support. More...

     #include <QSqlRelationalTableModel>

Inherits: QSqlTableModel.

- List of all members, including inherited members

## Public Types

enum | JoinMode { InnerJoin, LeftJoin }

## Public Functions

| QSqlRelationalTableModel ( QObject * parent = 0, QSqlDatabase db = QSqlDatabase() )
virtual | ~QSqlRelationalTableModel ()
QSqlRelation | relation ( int column ) const
virtual QSqlTableModel * | relationModel ( int column ) const
void | setJoinMode ( QSqlRelationalTableModel::JoinMode joinMode )
virtual void | setRelation ( int column, const QSqlRelation & relation )

## Reimplemented Public Functions

virtual void | clear ()
virtual QVariant | data ( const QModelIndex & index, int role = Qt::DisplayRole ) const
virtual bool | removeColumns ( int column, int count, const QModelIndex & parent = QModelIndex() )
virtual bool | select ()
virtual bool | setData ( const QModelIndex & index, const QVariant & value, int role = Qt::EditRole )
virtual void | setTable ( const QString & table )

- 25 public functions inherited from QSqlTableModel
- 16 public functions inherited from QSqlQueryModel
- 2 public functions inherited from QAbstractTableModel
- 35 public functions inherited from QAbstractItemModel
- 29 public functions inherited from QObject

## Public Slots

virtual void | revertRow ( int row )

- 4 public slots inherited from QSqlTableModel
- 2 public slots inherited from QAbstractItemModel
- 1 public slot inherited from QObject

## Reimplemented Protected Functions

virtual bool | insertRowIntoTable ( const QSqlRecord & values )
virtual QString | orderByClause () const
virtual QString | selectStatement () const
virtual bool | updateRowInTable ( int row, const QSqlRecord & values )

- 8 protected functions inherited from QSqlTableModel
- 3 protected functions inherited from QSqlQueryModel
- 21 protected functions inherited from QAbstractItemModel
- 8 protected functions inherited from QObject

### Additional Inherited Members

- 1 property inherited from QObject
- 4 signals inherited from QSqlTableModel
- 18 signals inherited from QAbstractItemModel
- 1 signal inherited from QObject
- 7 static public members inherited from QObject
- 8 protected functions inherited from QSqlTableModel
- 3 protected functions inherited from QSqlQueryModel
- 21 protected functions inherited from QAbstractItemModel
- 8 protected functions inherited from QObject
- 1 protected slot inherited from QAbstractItemModel

## Detailed Description

The QSqlRelationalTableModel class provides an editable data model for a single database table, with foreign key support.

QSqlRelationalTableModel acts like QSqlTableModel, but allows columns to be set as foreign keys into other database tables.

The screenshot on the left shows a plain QSqlTableModel in a QTableView. Foreign keys (`city` and `country`) aren't resolved to human-readable values. The screenshot on the right shows a QSqlRelationalTableModel, with foreign keys resolved into human-readable text strings.

The following code snippet shows how the QSqlRelationalTableModel was set up:

         model->setTable("employee");

         model->setRelation(2, QSqlRelation("city", "id", "name"));
         model->setRelation(3, QSqlRelation("country", "id", "name"));

The setRelation() function calls establish a relationship between two tables. The first call specifies that column 2 in table `employee` is a foreign key that maps with field `id` of table `city`, and that the view should present the `city`'s `name` field to the user. The second call does something similar with column 3.

If you use a read-write QSqlRelationalTableModel, you probably want to use QSqlRelationalDelegate on the view. Unlike the default delegate, QSqlRelationalDelegate provides a combobox for fields that are foreign keys into other tables. To use the class, simply call QAbstractItemView::setItemDelegate() on the view with an instance of QSqlRelationalDelegate:

         QTableView *view = new QTableView;
         view->setModel(model);
         view->setItemDelegate(new QSqlRelationalDelegate(view));

The sql/relationaltablemodel example illustrates how to use QSqlRelationalTableModel in conjunction with QSqlRelationalDelegate to provide tables with foreign key support.

Notes:

- The table must have a primary key declared.
- The table's primary key may not contain a relation to another table.
- If a relational table contains keys that refer to non-existent rows in the referenced table, the rows containing the invalid keys will not be exposed through the model. The user or the database is responsible for keeping referential integrity.
- If a relation's display column name is also used as a column name in the main table, or if it is used as display column name in more than one relation it will be aliased. The alias is is the relation's table name and display column name joined by an underscore (e.g. tablename_columnname). All occurrences of the duplicate display column name are aliased when duplication is detected, but no aliasing is done to the column names in the main table. The aliasing doesn't affect QSqlRelation, so QSqlRelation::displayColumn() will return the original display column name, but QSqlRecord::fieldName() will return aliases.
- When using setData() the role should always be Qt::EditRole, and when using data() the role should always be Qt::DisplayRole.

See also QSqlRelation, QSqlRelationalDelegate, and Relational Table Model Example.

## Member Type Documentation

### enum QSqlRelationalTableModel::JoinMode

This enum specifies the type of mode to use when joining two tables.

Constant | Value | Description
--- | --- | ---
`QSqlRelationalTableModel::InnerJoin` | `0` | Inner join mode, return rows when there is at least one match in both tables.
`QSqlRelationalTableModel::LeftJoin` | `1` | Left join mode, returns all rows from the left table (table_name1), even if there are no matches in the right table (table_name2).

This enum was introduced or modified in Qt 4.8.

See also QSqlRelationalTableModel::setJoinMode().

## Member Function Documentation

### QSqlRelationalTableModel::QSqlRelationalTableModel ( QObject * parent = 0, QSqlDatabase db = QSqlDatabase() )

Creates an empty QSqlRelationalTableModel and sets the parent to parent and the database connection to db. If db is not valid, the default database connection will be used.

### QSqlRelationalTableModel::~QSqlRelationalTableModel ()`[virtual]`

Destroys the object and frees any allocated resources.

### void QSqlRelationalTableModel::clear ()`[virtual]`

Reimplemented from QSqlQueryModel::clear().

### QVariant QSqlRelationalTableModel::data ( const QModelIndex & index, int role = Qt::DisplayRole ) const`[virtual]`

Reimplemented from QAbstractItemModel::data().

See also setData().

### bool QSqlRelationalTableModel::insertRowIntoTable ( const QSqlRecord & values )`[virtual protected]`

Reimplemented from QSqlTableModel::insertRowIntoTable().

### QString QSqlRelationalTableModel::orderByClause () const`[virtual protected]`

Reimplemented from QSqlTableModel::orderByClause().

### QSqlRelation QSqlRelationalTableModel::relation ( int column ) const

Returns the relation for the column column, or an invalid relation if no relation is set.

See also setRelation() and QSqlRelation::isValid().

### QSqlTableModel * QSqlRelationalTableModel::relationModel ( int column ) const`[virtual]`

Returns a QSqlTableModel object for accessing the table for which column is a foreign key, or 0 if there is no relation for the given column.

The returned object is owned by the QSqlRelationalTableModel.

See also setRelation() and relation().

### bool QSqlRelationalTableModel::removeColumns ( int column, int count, const QModelIndex & parent = QModelIndex() )`[virtual]`

Reimplemented from QAbstractItemModel::removeColumns().

### void QSqlRelationalTableModel::revertRow ( int row )`[virtual slot]`

Reimplemented from QSqlTableModel::revertRow().

### bool QSqlRelationalTableModel::select ()`[virtual]`

Reimplemented from QSqlTableModel::select().

### QString QSqlRelationalTableModel::selectStatement () const`[virtual protected]`

Reimplemented from QSqlTableModel::selectStatement().

### bool QSqlRelationalTableModel::setData ( const QModelIndex & index, const QVariant & value, int role = Qt::EditRole )`[virtual]`

Reimplemented from QAbstractItemModel::setData().

Sets the data for the role in the item with the specified index to the value given. Depending on the edit strategy, the value might be applied to the database at once, or it may be cached in the model.

Returns true if the value could be set, or false on error (for example, if index is out of bounds).

For relational columns, value must be the index, not the display value. The index must also exist in the referenced table, otherwise the function returns false.

See also editStrategy(), data(), submit(), and revertRow().

### void QSqlRelationalTableModel::setJoinMode ( QSqlRelationalTableModel::JoinMode joinMode )

Sets the SQL join mode to the value given by joinMode to show or hide rows with NULL foreign keys.

In InnerJoin mode (the default) these rows will not be shown; use the LeftJoin mode if you want to show them.

This function was introduced in Qt 4.8.

See also QSqlRelationalTableModel::JoinMode.

### void QSqlRelationalTableModel::setRelation ( int column, const QSqlRelation & relation )`[virtual]`

Lets the specified column be a foreign index specified by relation.

Example:

         model->setTable("employee");

         model->setRelation(2, QSqlRelation("city", "id", "name"));

The setRelation() call specifies that column 2 in table `employee` is a foreign key that maps with field `id` of table `city`, and that the view should present the `city`'s `name` field to the user.

Note: The table's primary key may not contain a relation to another table.

See also relation().

### void QSqlRelationalTableModel::setTable ( const QString & table )`[virtual]`

Reimplemented from QSqlTableModel::setTable().

### bool QSqlRelationalTableModel::updateRowInTable ( int row, const QSqlRecord & values )`[virtual protected]`

Reimplemented from QSqlTableModel::updateRowInTable().