- Qt 6.6
- Qt SQL
- C++ Classes
- QSqlDatabase
- Qt 6.6.2 Reference Documentation

# QSqlDatabase Class

The QSqlDatabase class handles a connection to a database. More...

Header: | #include <QSqlDatabase>
CMake: | find_package(Qt6 REQUIRED COMPONENTS Sql) target_link_libraries(mytarget PRIVATE Qt6::Sql)
qmake: | QT += sql

- List of all members, including inherited members
- Deprecated members
- QSqlDatabase is part of Database Classes.

## Public Functions

| QSqlDatabase()
| QSqlDatabase(const QSqlDatabase &other)
| ~QSqlDatabase()
void | close()
bool | commit()
QString | connectOptions() const
QString | connectionName() const
QString | databaseName() const
QSqlDriver * | driver() const
QString | driverName() const
QString | hostName() const
bool | isOpen() const
bool | isOpenError() const
bool | isValid() const
QSqlError | lastError() const
QSql::NumericalPrecisionPolicy | numericalPrecisionPolicy() const
bool | open()
bool | open(const QString &user, const QString &password)
QString | password() const
int | port() const
QSqlIndex | primaryIndex(const QString &tablename) const
QSqlRecord | record(const QString &tablename) const
bool | rollback()
void | setConnectOptions(const QString &options = QString())
void | setDatabaseName(const QString &name)
void | setHostName(const QString &host)
void | setNumericalPrecisionPolicy(QSql::NumericalPrecisionPolicy precisionPolicy)
void | setPassword(const QString &password)
void | setPort(int port)
void | setUserName(const QString &name)
QStringList | tables(QSql::TableType type = QSql::Tables) const
bool | transaction()
QString | userName() const
QSqlDatabase & | operator=(const QSqlDatabase &other)

## Static Public Members

QSqlDatabase | addDatabase(const QString &type, const QString &connectionName = QLatin1StringView(defaultConnection))
QSqlDatabase | addDatabase(QSqlDriver *driver, const QString &connectionName = QLatin1StringView(defaultConnection))
QSqlDatabase | cloneDatabase(const QSqlDatabase &other, const QString &connectionName)
QSqlDatabase | cloneDatabase(const QString &other, const QString &connectionName)
QStringList | connectionNames()
bool | contains(const QString &connectionName = QLatin1StringView(defaultConnection))
QSqlDatabase | database(const QString &connectionName = QLatin1StringView(defaultConnection), bool open = true)
QStringList | drivers()
bool | isDriverAvailable(const QString &name)
void | registerSqlDriver(const QString &name, QSqlDriverCreatorBase *creator)
void | removeDatabase(const QString &connectionName)

## Protected Functions

| QSqlDatabase(const QString &type)
| QSqlDatabase(QSqlDriver *driver)

## Detailed Description

The QSqlDatabase class provides an interface for accessing a database through a connection. An instance of QSqlDatabase represents the connection. The connection provides access to the database via one of the supported database drivers, which are derived from QSqlDriver. Alternatively, you can subclass your own database driver from QSqlDriver. See How to Write Your Own Database Driver for more information.

Create a connection (i.e., an instance of QSqlDatabase) by calling one of the static addDatabase() functions, where you specify the driver or type of driver to use (depending on the type of database) and a connection name. A connection is known by its own name, not by the name of the database it connects to. You can have multiple connections to one database. QSqlDatabase also supports the concept of a default connection, which is the unnamed connection. To create the default connection, don't pass the connection name argument when you call addDatabase(). Subsequently, the default connection will be assumed if you call any static member function without specifying the connection name. The following snippet shows how to create and open a default connection to a PostgreSQL database:

         QSqlDatabase db = QSqlDatabase::addDatabase("QPSQL");
         db.setHostName("acidalia");
         db.setDatabaseName("customdb");
         db.setUserName("mojito");
         db.setPassword("J0a1m8");
         bool ok = db.open();

Once the QSqlDatabase object has been created, set the connection parameters with setDatabaseName(), setUserName(), setPassword(), setHostName(), setPort(), and setConnectOptions(). Then call open() to activate the physical connection to the database. The connection is not usable until you open it.

The connection defined above will be the default connection, because we didn't give a connection name to addDatabase(). Subsequently, you can get the default connection by calling database() without the connection name argument:

         QSqlDatabase db = QSqlDatabase::database();

QSqlDatabase is a value class. Changes made to a database connection via one instance of QSqlDatabase will affect other instances of QSqlDatabase that represent the same connection. Use cloneDatabase() to create an independent database connection based on an existing one.

Warning: It is highly recommended that you do not keep a copy of the QSqlDatabase around as a member of a class, as this will prevent the instance from being correctly cleaned up on shutdown. If you need to access an existing QSqlDatabase, it should be accessed with database(). If you chose to have a QSqlDatabase member variable, this needs to be deleted before the QCoreApplication instance is deleted, otherwise it may lead to undefined behavior.

If you create multiple database connections, specify a unique connection name for each one, when you call addDatabase(). Use database() with a connection name to get that connection. Use removeDatabase() with a connection name to remove a connection. QSqlDatabase outputs a warning if you try to remove a connection referenced by other QSqlDatabase objects. Use contains() to see if a given connection name is in the list of connections.

Some utility methods:
tables() | returns the list of tables
primaryIndex() | returns a table's primary index
record() | returns meta-information about a table's fields
transaction() | starts a transaction
commit() | saves and completes a transaction
rollback() | cancels a transaction
hasFeature() | checks if a driver supports transactions
lastError() | returns information about the last error
drivers() | returns the names of the available SQL drivers
isDriverAvailable() | checks if a particular driver is available
registerSqlDriver() | registers a custom-made driver

Note: When using transactions, you must start the transaction before you create your query.

See also QSqlDriver, QSqlQuery, Qt SQL, and Threads and the SQL Module.

## Member Function Documentation

### QSqlDatabase::QSqlDatabase()

Creates an empty, invalid QSqlDatabase object. Use addDatabase(), removeDatabase(), and database() to get valid QSqlDatabase objects.

### `[explicit protected]` QSqlDatabase::QSqlDatabase(const QString &type)

This is an overloaded function.

Creates a QSqlDatabase connection that uses the driver referred to by type. If the type is not recognized, the database connection will have no functionality.

The currently available driver types are:

Driver Type | Description
--- | ---
QDB2 | IBM DB2
QIBASE | Borland InterBase Driver
QMYSQL | MySQL Driver
QOCI | Oracle Call Interface Driver
QODBC | ODBC Driver (includes Microsoft SQL Server)
QPSQL | PostgreSQL Driver
QSQLITE | SQLite version 3 or above
QMIMER | Mimer SQL 11 or above

Additional third party drivers, including your own custom drivers, can be loaded dynamically.

See also SQL Database Drivers, registerSqlDriver(), and drivers().

### `[explicit protected]` QSqlDatabase::QSqlDatabase(QSqlDriver *driver)

This is an overloaded function.

Creates a database connection using the given driver.

### QSqlDatabase::QSqlDatabase(const QSqlDatabase &other)

Creates a copy of other.

### `[noexcept]` QSqlDatabase::~QSqlDatabase()

Destroys the object and frees any allocated resources.

Note: When the last connection is destroyed, the destructor implicitly calls close() to release the database connection.

See also close().

### `[static]` QSqlDatabase QSqlDatabase::addDatabase(const QString &type, const QString &connectionName = QLatin1StringView(defaultConnection))

Adds a database to the list of database connections using the driver type and the connection name connectionName. If there already exists a database connection called connectionName, that connection is removed.

The database connection is referred to by connectionName. The newly added database connection is returned.

If type is not available or could not be loaded, isValid() returns `false`.

If connectionName is not specified, the new connection becomes the default connection for the application, and subsequent calls to database() without the connection name argument will return the default connection. If a connectionName is provided here, use database(connectionName) to retrieve the connection.

Warning: If you add a connection with the same name as an existing connection, the new connection replaces the old one. If you call this function more than once without specifying connectionName, the default connection will be the one replaced.

Before using the connection, it must be initialized. e.g., call some or all of setDatabaseName(), setUserName(), setPassword(), setHostName(), setPort(), and setConnectOptions(), and, finally, open().

Note: This function is thread-safe.

See also database(), removeDatabase(), and Threads and the SQL Module.

### `[static]` QSqlDatabase QSqlDatabase::addDatabase(QSqlDriver *driver, const QString &connectionName = QLatin1StringView(defaultConnection))

This overload is useful when you want to create a database connection with a driver you instantiated yourself. It might be your own database driver, or you might just need to instantiate one of the Qt drivers yourself. If you do this, it is recommended that you include the driver code in your application. For example, you can create a PostgreSQL connection with your own QPSQL driver like this:

     PGconn *con = PQconnectdb("host=server user=bart password=simpson dbname=springfield");
     QPSQLDriver *drv = new QPSQLDriver(con);
     QSqlDatabase db = QSqlDatabase::addDatabase(drv); // becomes the new default connection
     QSqlQuery query;
     query.exec("SELECT NAME, ID FROM STAFF");

The above code sets up a PostgreSQL connection and instantiates a QPSQLDriver object. Next, addDatabase() is called to add the connection to the known connections so that it can be used by the Qt SQL classes. When a driver is instantiated with a connection handle (or set of handles), Qt assumes that you have already opened the database connection.

Note: We assume that `qtdir` is the directory where Qt is installed. This will pull in the code that is needed to use the PostgreSQL client library and to instantiate a QPSQLDriver object, assuming that you have the PostgreSQL headers somewhere in your include search path.

Remember that you must link your application against the database client library. Make sure the client library is in your linker's search path, and add lines like these to your `.pro` file:

     unix:LIBS += -lpq
     win32:LIBS += libpqdll.lib

The method described works for all the supplied drivers. The only difference will be in the driver constructor arguments. Here is a table of the drivers included with Qt, their source code files, and their constructor arguments:

Driver | Class name | Constructor arguments | File to include
--- | --- | --- | ---
QPSQL | QPSQLDriver | PGconn *connection | `qsql_psql.cpp`
QMYSQL | QMYSQLDriver | MYSQL *connection | `qsql_mysql.cpp`
QOCI | QOCIDriver | OCIEnv *environment, OCISvcCtx *serviceContext | `qsql_oci.cpp`
QODBC | QODBCDriver | SQLHANDLE environment, SQLHANDLE connection | `qsql_odbc.cpp`
QDB2 | QDB2 | SQLHANDLE environment, SQLHANDLE connection | `qsql_db2.cpp`
QSQLITE | QSQLiteDriver | sqlite *connection | `qsql_sqlite.cpp`
QMIMER | QMimerSQLDriver | MimerSession *connection | `qsql_mimer.cpp`
QIBASE | QIBaseDriver | isc_db_handle connection | `qsql_ibase.cpp`

Warning: Adding a database connection with the same connection name as an existing connection, causes the existing connection to be replaced by the new one.

Warning: The SQL framework takes ownership of the driver. It must not be deleted. To remove the connection, use removeDatabase().

See also drivers().

### `[static]` QSqlDatabase QSqlDatabase::cloneDatabase(const QSqlDatabase &other, const QString &connectionName)

Clones the database connection other and stores it as connectionName. All the settings from the original database, e.g. databaseName(), hostName(), etc., are copied across. Does nothing if other is an invalid database. Returns the newly created database connection.

Note: The new connection has not been opened. Before using the new connection, you must call open().

Note: This function is reentrant.

### `[static]` QSqlDatabase QSqlDatabase::cloneDatabase(const QString &other, const QString &connectionName)

This is an overloaded function.

Clones the database connection other and stores it as connectionName. All the settings from the original database, e.g. databaseName(), hostName(), etc., are copied across. Does nothing if other is an invalid database. Returns the newly created database connection.

Note: The new connection has not been opened. Before using the new connection, you must call open().

This overload is useful when cloning the database in another thread to the one that is used by the database represented by other.

### void QSqlDatabase::close()

Closes the database connection, freeing any resources acquired, and invalidating any existing QSqlQuery objects that are used with the database.

This will also affect copies of this QSqlDatabase object.

See also removeDatabase().

### bool QSqlDatabase::commit()

Commits a transaction to the database if the driver supports transactions and a transaction() has been started. Returns `true` if the operation succeeded. Otherwise it returns `false`.

Note: For some databases, the commit will fail and return `false` if there is an active query using the database for a `SELECT`. Make the query inactive before doing the commit.

Call lastError() to get information about errors.

See also QSqlQuery::isActive(), QSqlDriver::hasFeature(), and rollback().

### QString QSqlDatabase::connectOptions() const

Returns the connection options string used for this connection. The string may be empty.

See also setConnectOptions().

### QString QSqlDatabase::connectionName() const

Returns the connection name, which may be empty.

Note: The connection name is not the database name.

See also addDatabase().

### `[static]` QStringList QSqlDatabase::connectionNames()

Returns a list containing the names of all connections.

Note: This function is thread-safe.

See also contains(), database(), and Threads and the SQL Module.

### `[static]` bool QSqlDatabase::contains(const QString &connectionName = QLatin1StringView(defaultConnection))

Returns `true` if the list of database connections contains connectionName; otherwise returns `false`.

Note: This function is thread-safe.

See also connectionNames(), database(), and Threads and the SQL Module.

### `[static]` QSqlDatabase QSqlDatabase::database(const QString &connectionName = QLatin1StringView(defaultConnection), bool open = true)

Returns the database connection called connectionName. The database connection must have been previously added with addDatabase(). If open is true (the default) and the database connection is not already open it is opened now. If no connectionName is specified the default connection is used. If connectionName does not exist in the list of databases, an invalid connection is returned.

Note: This function is thread-safe.

See also isOpen() and Threads and the SQL Module.

### QString QSqlDatabase::databaseName() const

Returns the connection's database name, which may be empty.

Note: The database name is not the connection name.

See also setDatabaseName().

### QSqlDriver *QSqlDatabase::driver() const

Returns the database driver used to access the database connection.

See also addDatabase() and drivers().

### QString QSqlDatabase::driverName() const

Returns the connection's driver name.

See also addDatabase() and driver().

### `[static]` QStringList QSqlDatabase::drivers()

Returns a list of all the available database drivers.

See also registerSqlDriver().

### QString QSqlDatabase::hostName() const

Returns the connection's host name; it may be empty.

See also setHostName().

### `[static]` bool QSqlDatabase::isDriverAvailable(const QString &name)

Returns `true` if a driver called name is available; otherwise returns `false`.

See also drivers().

### bool QSqlDatabase::isOpen() const

Returns `true` if the database connection is currently open; otherwise returns `false`.

### bool QSqlDatabase::isOpenError() const

Returns `true` if there was an error opening the database connection; otherwise returns `false`. Error information can be retrieved using the lastError() function.

### bool QSqlDatabase::isValid() const

Returns `true` if the QSqlDatabase has a valid driver.

Example:

     QSqlDatabase db;
     qDebug() << db.isValid();    // Returns false

     db = QSqlDatabase::database("sales");
     qDebug() << db.isValid();    // Returns \c true if "sales" connection exists

     QSqlDatabase::removeDatabase("sales");
     qDebug() << db.isValid();    // Returns false

### QSqlError QSqlDatabase::lastError() const

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

Failures that occur in conjunction with an individual query are reported by QSqlQuery::lastError().

See also QSqlError and QSqlQuery::lastError().

### QSql::NumericalPrecisionPolicy QSqlDatabase::numericalPrecisionPolicy() const

Returns the current default precision policy for the database connection.

See also QSql::NumericalPrecisionPolicy, setNumericalPrecisionPolicy(), QSqlQuery::numericalPrecisionPolicy(), and QSqlQuery::setNumericalPrecisionPolicy().

### bool QSqlDatabase::open()

Opens the database connection using the current connection values. Returns `true` on success; otherwise returns `false`. Error information can be retrieved using lastError().

See also lastError(), setDatabaseName(), setUserName(), setPassword(), setHostName(), setPort(), and setConnectOptions().

### bool QSqlDatabase::open(const QString &user, const QString &password)

This is an overloaded function.

Opens the database connection using the given user name and password. Returns `true` on success; otherwise returns `false`. Error information can be retrieved using the lastError() function.

This function does not store the password it is given. Instead, the password is passed directly to the driver for opening the connection and it is then discarded.

See also lastError().

### QString QSqlDatabase::password() const

Returns the connection's password. An empty string will be returned if the password was not set with setPassword(), and if the password was given in the open() call, or if no password was used.

See also setPassword().

### int QSqlDatabase::port() const

Returns the connection's port number. The value is undefined if the port number has not been set.

See also setPort().

### QSqlIndex QSqlDatabase::primaryIndex(const QString &tablename) const

Returns the primary index for table tablename. If no primary index exists, an empty QSqlIndex is returned.

Note: Some drivers, such as the QPSQL driver, may may require you to pass tablename in lower case if the table was not quoted when created. See the Qt SQL driver documentation for more information.

See also tables() and record().

### QSqlRecord QSqlDatabase::record(const QString &tablename) const

Returns a QSqlRecord populated with the names of all the fields in the table (or view) called tablename. The order in which the fields appear in the record is undefined. If no such table (or view) exists, an empty record is returned.

Note: Some drivers, such as the QPSQL driver, may may require you to pass tablename in lower case if the table was not quoted when created. See the Qt SQL driver documentation for more information.

### `[static]` void QSqlDatabase::registerSqlDriver(const QString &name, QSqlDriverCreatorBase *creator)

This function registers a new SQL driver called name, within the SQL framework. This is useful if you have a custom SQL driver and don't want to compile it as a plugin.

Example:

     QSqlDatabase::registerSqlDriver("MYDRIVER", new QSqlDriverCreator<QSqlDriver>);
     QVERIFY(QSqlDatabase::drivers().contains("MYDRIVER"));
     QSqlDatabase db = QSqlDatabase::addDatabase("MYDRIVER");
     QVERIFY(db.isValid());

QSqlDatabase takes ownership of the creator pointer, so you mustn't delete it yourself.

See also drivers().

### `[static]` void QSqlDatabase::removeDatabase(const QString &connectionName)

Removes the database connection connectionName from the list of database connections.

Warning: There should be no open queries on the database connection when this function is called, otherwise a resource leak will occur.

Example:

     // WRONG
     QSqlDatabase db = QSqlDatabase::database("sales");
     QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db);
     QSqlDatabase::removeDatabase("sales"); // will output a warning
     // "db" is now a dangling invalid database connection,
     // "query" contains an invalid result set

The correct way to do it:

     {
         QSqlDatabase db = QSqlDatabase::database("sales");
         QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db);
     }
     // Both "db" and "query" are destroyed because they are out of scope
     QSqlDatabase::removeDatabase("sales"); // correct

To remove the default connection, which may have been created with a call to addDatabase() not specifying a connection name, you can retrieve the default connection name by calling connectionName() on the database returned by database(). Note that if a default database hasn't been created an invalid database will be returned.

Note: This function is thread-safe.

See also database(), connectionName(), and Threads and the SQL Module.

### bool QSqlDatabase::rollback()

Rolls back a transaction on the database, if the driver supports transactions and a transaction() has been started. Returns `true` if the operation succeeded. Otherwise it returns `false`.

Note: For some databases, the rollback will fail and return `false` if there is an active query using the database for a `SELECT`. Make the query inactive before doing the rollback.

Call lastError() to get information about errors.

See also QSqlQuery::isActive(), QSqlDriver::hasFeature(), and commit().

### void QSqlDatabase::setConnectOptions(const QString &options = QString())

Sets database-specific options. This must be done before the connection is opened, otherwise it has no effect. Another possibility is to close the connection, call QSqlDatabase::setConnectOptions(), and open() the connection again.

The format of the options string is a semicolon separated list of option names or option=value pairs. The options depend on the database client used and are described for each plugin in the SQL Database Drivers page.

Examples:

     db.setConnectOptions("SSL_KEY=client-key.pem;SSL_CERT=client-cert.pem;SSL_CA=ca-cert.pem;CLIENT_IGNORE_SPACE=1"); // use an SSL connection to the server
     if (!db.open()) {
         db.setConnectOptions(); // clears the connect option string
         // ...
     }
     // ...
     // PostgreSQL connection
     db.setConnectOptions("requiressl=1"); // enable PostgreSQL SSL connections
     if (!db.open()) {
         db.setConnectOptions(); // clear options
         // ...
     }
     // ...
     // ODBC connection
     db.setConnectOptions("SQL_ATTR_ACCESS_MODE=SQL_MODE_READ_ONLY;SQL_ATTR_TRACE=SQL_OPT_TRACE_ON"); // set ODBC options
     if (!db.open()) {
         db.setConnectOptions(); // don't try to set this option
         // ...
     }
     }

Refer to the client library documentation for more information about the different options.

See also connectOptions().

### void QSqlDatabase::setDatabaseName(const QString &name)

Sets the connection's database name to name. To have effect, the database name must be set before the connection is opened. Alternatively, you can close() the connection, set the database name, and call open() again.

Note: The database name is not the connection name. The connection name must be passed to addDatabase() at connection object create time.

For the QSQLITE driver, if the database name specified does not exist, then it will create the file for you unless the QSQLITE_OPEN_READONLY option is set.

Additionally, name can be set to `":memory:"` which will create a temporary database which is only available for the lifetime of the application.

For the QOCI (Oracle) driver, the database name is the TNS Service Name.

For the QODBC driver, the name can either be a DSN, a DSN filename (in which case the file must have a `.dsn` extension), or a connection string.

For example, Microsoft Access users can use the following connection string to open an `.mdb` file directly, instead of having to create a DSN entry in the ODBC manager:

     // ...
     QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
     db.setDatabaseName("DRIVER={Microsoft Access Driver (*.mdb, *.accdb)};FIL={MS Access};DBQ=myaccessfile.mdb");
     if (db.open()) {
         // success!
     }
     // ...

There is no default value.

See also databaseName(), setUserName(), setPassword(), setHostName(), setPort(), setConnectOptions(), and open().

### void QSqlDatabase::setHostName(const QString &host)

Sets the connection's host name to host. To have effect, the host name must be set before the connection is opened. Alternatively, you can close() the connection, set the host name, and call open() again.

There is no default value.

See also hostName(), setUserName(), setPassword(), setDatabaseName(), setPort(), setConnectOptions(), and open().

### void QSqlDatabase::setNumericalPrecisionPolicy(QSql::NumericalPrecisionPolicy precisionPolicy)

Sets the default numerical precision policy used by queries created on this database connection to precisionPolicy.

Note: Drivers that don't support fetching numerical values with low precision will ignore the precision policy. You can use QSqlDriver::hasFeature() to find out whether a driver supports this feature.

Note: Setting the default precision policy to precisionPolicy doesn't affect any currently active queries.

See also QSql::NumericalPrecisionPolicy, numericalPrecisionPolicy(), QSqlQuery::setNumericalPrecisionPolicy(), and QSqlQuery::numericalPrecisionPolicy().

### void QSqlDatabase::setPassword(const QString &password)

Sets the connection's password to password. To have effect, the password must be set before the connection is opened. Alternatively, you can close() the connection, set the password, and call open() again.

There is no default value.

Warning: This function stores the password in plain text within Qt. Use the open() call that takes a password as parameter to avoid this behavior.

See also password(), setUserName(), setDatabaseName(), setHostName(), setPort(), setConnectOptions(), and open().

### void QSqlDatabase::setPort(int port)

Sets the connection's port number to port. To have effect, the port number must be set before the connection is opened. Alternatively, you can close() the connection, set the port number, and call open() again..

There is no default value.

See also port(), setUserName(), setPassword(), setHostName(), setDatabaseName(), setConnectOptions(), and open().

### void QSqlDatabase::setUserName(const QString &name)

Sets the connection's user name to name. To have effect, the user name must be set before the connection is opened. Alternatively, you can close() the connection, set the user name, and call open() again.

There is no default value.

See also userName(), setDatabaseName(), setPassword(), setHostName(), setPort(), setConnectOptions(), and open().

### QStringList QSqlDatabase::tables(QSql::TableType type = QSql::Tables) const

Returns a list of the database's tables, system tables and views, as specified by the parameter type.

See also primaryIndex() and record().

### bool QSqlDatabase::transaction()

Begins a transaction on the database if the driver supports transactions. Returns `true` if the operation succeeded. Otherwise it returns `false`.

See also QSqlDriver::hasFeature(), commit(), and rollback().

### QString QSqlDatabase::userName() const

Returns the connection's user name; it may be empty.

See also setUserName().

### QSqlDatabase &QSqlDatabase::operator=(const QSqlDatabase &other)

Assigns other to this object.