Presenting Data in a Table View¶
The
QSqlQueryModel
,QSqlTableModel
, andQSqlRelationalTableModel
classes can be used as a data source for Qt’s view classes such asQListView
,QTableView
, andQTreeView
. In practice,QTableView
is by far the most common choice, because an SQL result set is essentially a two-dimensional data structure.The following example creates a view based on an SQL data model:
QTableView *view = new QTableView; view->setModel(model); view->show();If the model is a read-write model (e.g.,
QSqlTableModel
), the view lets the user edit the fields. You can disable this by callingview->setEditTriggers(QAbstractItemView::NoEditTriggers);You can use the same model as a data source for multiple views. If the user edits the model through one of the views, the other views will reflect the changes immediately. The Table Model example shows how it works.
View classes display a header at the top to label the columns. To change the header texts, call
setHeaderData()
on the model. The header’s labels default to the table’s field names. For example:model.setHeaderData(0, Qt.Horizontal, QObject::tr("ID")) model.setHeaderData(1, Qt.Horizontal, QObject::tr("Name")) model.setHeaderData(2, Qt.Horizontal, QObject::tr("City")) model.setHeaderData(3, Qt.Horizontal, QObject::tr("Country"))
QTableView
also has a vertical header on the left with numbers identifying the rows. If you insert rows programmatically usinginsertRows()
, the new rows will be marked with an asterisk (*) until they are submitted usingsubmitAll()
or automatically when the user moves to another record (assuming theedit strategy
isOnRowChange
).Likewise, if you remove rows using
removeRows()
, the rows will be marked with an exclamation mark (!) until the change is submitted.The items in the view are rendered using a delegate. The default delegate,
QItemDelegate
, handles the most common data types (int
,QString
,QImage
, etc.). The delegate is also responsible for providing editor widgets (e.g., a combobox) when the user starts editing an item in the view. You can create your own delegates by subclassingQAbstractItemDelegate
orQItemDelegate
. See Model/View Programming for more information.
QSqlTableModel
is optimized to operate on a single table at a time. If you need a read-write model that operates on an arbitrary result set, you can subclassQSqlQueryModel
and reimplementflags()
andsetData()
to make it read-write. The following two functions make fields 1 and 2 of a query model editable:Qt::ItemFlags EditableSqlModel::flags( const QModelIndex &index) const { Qt::ItemFlags flags = QSqlQueryModel::flags(index); if (index.column() == 1 || index.column() == 2) flags |= Qt::ItemIsEditable; return flags; } bool EditableSqlModel::setData(const QModelIndex &index, const QVariant &value, int /* role */) { if (index.column() < 1 || index.column() > 2) return false; QModelIndex primaryKeyIndex = QSqlQueryModel::index(index.row(), 0); int id = data(primaryKeyIndex).toInt(); clear(); bool ok; if (index.column() == 1) { ok = setFirstName(id, value.toString()); } else { ok = setLastName(id, value.toString()); } refresh(); return ok; }The setFirstName() helper function is defined as follows:
bool EditableSqlModel::setFirstName(int personId, const QString &firstName) { QSqlQuery query; query.prepare("update person set firstname = ? where id = ?"); query.addBindValue(firstName); query.addBindValue(personId); return query.exec(); }The setLastName() function is similar. See the Query Model example for the complete source code.
Subclassing a model makes it possible to customize it in many ways: You can provide tooltips for the items, change the background color, provide calculated values, provide different values for viewing and editing, handle null values specially, and more. See Model/View Programming as well as the
QAbstractItemView
reference documentation for details.If all you need is to resolve a foreign key to a more human-friendly string, you can use
QSqlRelationalTableModel
. For best results, you should also useQSqlRelationalDelegate
, a delegate that provides combobox editors for editing foreign keys.The Relational Table Model example illustrates how to use
QSqlRelationalTableModel
in conjunction withQSqlRelationalDelegate
to provide tables with foreign key support.
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