QSqlQueryModel Class | Qt SQL 5.6

Qt 5.6 | Qt SQL | C++ Classes | QSqlQueryModel

Qt 5.6.2 Reference Documentation

# QSqlQueryModel Class

The QSqlQueryModel class provides a read-only data model for SQL result sets. More...

Header: | #include <QSqlQueryModel>
qmake: | QT += sql
Inherited By: | QSqlTableModel

- List of all members, including inherited members

## Public Functions

| QSqlQueryModel(QObject *parent = Q_NULLPTR)
virtual | ~QSqlQueryModel()
bool | canFetchMore(const QModelIndex &parent = QModelIndex()) const
virtual void | clear()
int | columnCount(const QModelIndex &index = QModelIndex()) const
QVariant | data(const QModelIndex &item, int role = Qt::DisplayRole) const
void | fetchMore(const QModelIndex &parent = QModelIndex())
QVariant | headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const
bool | insertColumns(int column, int count, const QModelIndex &parent = QModelIndex())
QSqlError | lastError() const
QSqlQuery | query() const
QSqlRecord | record(int row) const
QSqlRecord | record() const
bool | removeColumns(int column, int count, const QModelIndex &parent = QModelIndex())
int | rowCount(const QModelIndex &parent = QModelIndex()) const
bool | setHeaderData(int section, Qt::Orientation orientation, const QVariant &value, int role = Qt::EditRole)
void | setQuery(const QSqlQuery &query)
void | setQuery(const QString &query, const QSqlDatabase &db = QSqlDatabase())

## Protected Functions

virtual QModelIndex | indexInQuery(const QModelIndex &item) const
virtual void | queryChange()
void | setLastError(const QSqlError &error)

## Detailed Description

The QSqlQueryModel class provides a read-only data model for SQL result sets.

QSqlQueryModel is a high-level interface for executing SQL statements and traversing the result set. It is built on top of the lower-level QSqlQuery and can be used to provide data to view classes such as QTableView. For example:

          QSqlQueryModel *model = new QSqlQueryModel;
          model->setQuery("SELECT name, salary FROM employee");
          model->setHeaderData(0, Qt::Horizontal, tr("Name"));
          model->setHeaderData(1, Qt::Horizontal, tr("Salary"));

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

We set the model's query, then we set up the labels displayed in the view header.

QSqlQueryModel can also be used to access a database programmatically, without binding it to a view:

          QSqlTableModel model;
          model.setTable("employee");
          model.select();
          int salary = model.record(4).value("salary").toInt();

The code snippet above extracts the `salary` field from record 4 in the result set of the query `SELECT * from employee`. Assuming that `salary` is column 2, we can rewrite the last line as follows:

          int salary = model.data(model.index(4, 2)).toInt();

The model is read-only by default. To make it read-write, you must subclass it and reimplement setData() and flags(). Another option is to use QSqlTableModel, which provides a read-write model based on a single database table.

The querymodel example illustrates how to use QSqlQueryModel to display the result of a query. It also shows how to subclass QSqlQueryModel to customize the contents of the data before showing it to the user, and how to create a read-write model based on QSqlQueryModel.

If the database doesn't return the number of selected rows in a query, the model will fetch rows incrementally. See fetchMore() for more information.

See also QSqlTableModel, QSqlRelationalTableModel, QSqlQuery, Model/View Programming, and Query Model Example.

## Member Function Documentation

### QSqlQueryModel::QSqlQueryModel(QObject *parent = Q_NULLPTR)

Creates an empty QSqlQueryModel with the given parent.

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

Destroys the object and frees any allocated resources.

See also clear().

### bool QSqlQueryModel::canFetchMore(const QModelIndex &parent = QModelIndex()) const

Returns `true` if it is possible to read more rows from the database. This only affects databases that don't report back the size of a query (see QSqlDriver::hasFeature()).

parent should always be an invalid QModelIndex.

This function was introduced in Qt 4.1.

See also fetchMore().

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

Clears the model and releases any acquired resource.

### int QSqlQueryModel::columnCount(const QModelIndex &index = QModelIndex()) const

### QVariant QSqlQueryModel::data(const QModelIndex &item, int role = Qt::DisplayRole) const

Returns the value for the specified item and role.

If item is out of bounds or if an error occurred, an invalid QVariant is returned.

See also lastError().

### void QSqlQueryModel::fetchMore(const QModelIndex &parent = QModelIndex())

Fetches more rows from a database. This only affects databases that don't report back the size of a query (see QSqlDriver::hasFeature()).

To force fetching of the entire result set, you can use the following:

      while (myModel->canFetchMore())
          myModel->fetchMore();

parent should always be an invalid QModelIndex.

This function was introduced in Qt 4.1.

See also canFetchMore().

### QVariant QSqlQueryModel::headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const

Returns the header data for the given role in the section of the header with the specified orientation.

See also setHeaderData().

### `[virtual protected]` QModelIndex QSqlQueryModel::indexInQuery(const QModelIndex &item) const

Returns the index of the value in the database result set for the given item in the model.

The return value is identical to item if no columns or rows have been inserted, removed, or moved around.

Returns an invalid model index if item is out of bounds or if item does not point to a value in the result set.

See also QSqlTableModel::indexInQuery(), insertColumns(), and removeColumns().

### bool QSqlQueryModel::insertColumns(int column, int count, const QModelIndex &parent = QModelIndex())

Inserts count columns into the model at position column. The parent parameter must always be an invalid QModelIndex, since the model does not support parent-child relationships.

Returns `true` if column is within bounds; otherwise returns `false`.

By default, inserted columns are empty. To fill them with data, reimplement data() and handle any inserted column separately:

      QVariant MyModel::data(const QModelIndex &item, int role) const
      {
          if (item.column() == m_specialColumnNo) {
              // handle column separately
          }
          return QSqlQueryModel::data(item, role);
      }

See also removeColumns().

### QSqlError QSqlQueryModel::lastError() const

Returns information about the last error that occurred on the database.

See also setLastError() and query().

### QSqlQuery QSqlQueryModel::query() const

Returns the QSqlQuery associated with this model.

See also setQuery().

### `[virtual protected]` void QSqlQueryModel::queryChange()

This virtual function is called whenever the query changes. The default implementation does nothing.

query() returns the new query.

See also query() and setQuery().

### QSqlRecord QSqlQueryModel::record(int row) const

Returns the record containing information about the fields of the current query. If row is the index of a valid row, the record will be populated with values from that row.

If the model is not initialized, an empty record will be returned.

See also QSqlRecord::isEmpty().

### QSqlRecord QSqlQueryModel::record() const

This is an overloaded function.

Returns an empty record containing information about the fields of the current query.

If the model is not initialized, an empty record will be returned.

See also QSqlRecord::isEmpty().

### bool QSqlQueryModel::removeColumns(int column, int count, const QModelIndex &parent = QModelIndex())

Removes count columns from the model starting from position column. The parent parameter must always be an invalid QModelIndex, since the model does not support parent-child relationships.

Removing columns effectively hides them. It does not affect the underlying QSqlQuery.

Returns `true` if the columns were removed; otherwise returns `false`.

### int QSqlQueryModel::rowCount(const QModelIndex &parent = QModelIndex()) const

If the database supports returning the size of a query (see QSqlDriver::hasFeature()), the number of rows of the current query is returned. Otherwise, returns the number of rows currently cached on the client.

parent should always be an invalid QModelIndex.

This function was introduced in Qt 4.1.

See also canFetchMore() and QSqlDriver::hasFeature().

### bool QSqlQueryModel::setHeaderData(int section, Qt::Orientation orientation, const QVariant &value, int role = Qt::EditRole)

Sets the caption for a horizontal header for the specified role to value. This is useful if the model is used to display data in a view (e.g., QTableView).

Returns `true` if orientation is Qt::Horizontal and the section refers to a valid section; otherwise returns false.

Note that this function cannot be used to modify values in the database since the model is read-only.

See also headerData() and data().

### `[protected]` void QSqlQueryModel::setLastError(const QSqlError &error)

Protected function which allows derived classes to set the value of the last error that occurred on the database to error.

See also lastError().

### void QSqlQueryModel::setQuery(const QSqlQuery &query)

Resets the model and sets the data provider to be the given query. Note that the query must be active and must not be isForwardOnly().

lastError() can be used to retrieve verbose information if there was an error setting the query.

Note: Calling setQuery() will remove any inserted columns.

See also query(), QSqlQuery::isActive(), QSqlQuery::setForwardOnly(), and lastError().

### void QSqlQueryModel::setQuery(const QString &query, const QSqlDatabase &db = QSqlDatabase())

This is an overloaded function.

Executes the query query for the given database connection db. If no database (or an invalid database) is specified, the default connection is used.

lastError() can be used to retrieve verbose information if there was an error setting the query.

Example:

      QSqlQueryModel model;
      model.setQuery("select * from MyTable");
      if (model.lastError().isValid())
          qDebug() << model.lastError();

See also query(), queryChange(), and lastError().