QSqlRelationalTableModel Class Reference
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Левый скриншот показывает QSqlTableModel в QTableView. Внешние ключи (city и country) не представлены удобочитаемыми значениями. 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 foreigh key support.
Примечания:
- 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.
Описание функций-членов
QSqlRelationalTableModel::QSqlRelationalTableModel ( QObject * parent = 0, QSqlDatabase db = QSqlDatabase() )
Creates an empty QSqlRelationalTableModel and sets the parent to parent and the database connection to db. Если db не является корректным, используется соединение по умолчанию.
QSqlRelationalTableModel::~QSqlRelationalTableModel () [virtual]
Удаляет объект и освобождает все выделенные ему ресурсы.
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::setData ( const QModelIndex & index, const QVariant & value, int role = Qt::EditRole ) [virtual]
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.
Переопределено из QAbstractItemModel.
See also editStrategy(), data(), submit(), and revertRow().
void QSqlRelationalTableModel::setRelation ( int column, const QSqlRelation & relation ) [virtual]
Lets the specified column be a foreign index specified by relation.
Пример:
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().
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