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# QSqlRelationalTableModel Class Reference
[QtSql module]

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

Inherits QSqlTableModel.

### Types

- enum JoinMode { InnerJoin, LeftJoin }

### Methods

- __init__ (self, QObject parent = None, QSqlDatabase db = QSqlDatabase())
- clear (self)
- QVariant data (self, QModelIndex index, int role = Qt.DisplayRole)
- bool insertRowIntoTable (self, QSqlRecord values)
- QString orderByClause (self)
- QSqlRelation relation (self, int column)
- QSqlTableModel relationModel (self, int column)
- bool removeColumns (self, int column, int count, QModelIndex parent = QModelIndex())
- revertRow (self, int row)
- bool select (self)
- QString selectStatement (self)
- bool setData (self, QModelIndex index, QVariant value, int role = Qt.EditRole)
- setJoinMode (self, JoinMode joinMode)
- setRelation (self, int column, QSqlRelation relation)
- setTable (self, QString tableName)
- bool updateRowInTable (self, int row, QSqlRecord values)

## 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.

## Type Documentation

### 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().

## Method Documentation

### QSqlRelationalTableModel.__init__ (self, QObject parent = None, QSqlDatabase db = QSqlDatabase())

The parent argument, if not None, causes self to be owned by Qt instead of PyQt.

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.clear (self)

Reimplemented from QSqlQueryModel.clear().

### QVariant QSqlRelationalTableModel.data (self, QModelIndex index, int role = Qt.DisplayRole)

Reimplemented from QAbstractItemModel.data().

See also setData().

### bool QSqlRelationalTableModel.insertRowIntoTable (self, QSqlRecord values)

Reimplemented from QSqlTableModel.insertRowIntoTable().

### QString QSqlRelationalTableModel.orderByClause (self)

Reimplemented from QSqlTableModel.orderByClause().

### QSqlRelation QSqlRelationalTableModel.relation (self, int column)

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 (self, int column)

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 (self, int column, int count, QModelIndex parent = QModelIndex())

Reimplemented from QAbstractItemModel.removeColumns().

### QSqlRelationalTableModel.revertRow (self, int row)

Reimplemented from QSqlTableModel.revertRow().

### bool QSqlRelationalTableModel.select (self)

Reimplemented from QSqlTableModel.select().

### QString QSqlRelationalTableModel.selectStatement (self)

Reimplemented from QSqlTableModel.selectStatement().

### bool QSqlRelationalTableModel.setData (self, QModelIndex index, QVariant value, int role = Qt.EditRole)

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().

### QSqlRelationalTableModel.setJoinMode (self, 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.

### QSqlRelationalTableModel.setRelation (self, int column, QSqlRelation relation)

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().

### QSqlRelationalTableModel.setTable (self, QString tableName)

Reimplemented from QSqlTableModel.setTable().

### bool QSqlRelationalTableModel.updateRowInTable (self, int row, QSqlRecord values)

Reimplemented from QSqlTableModel.updateRowInTable().