Connecting to Databases¶
To access a database with
QSqlQuery
orQSqlQueryModel
, create and open one or more database connections. Database connections are normally identified by connection name, not by database name. You can have multiple connections to the same database.QSqlDatabase
also supports the concept of a default connection, which is an unnamed connection. When callingQSqlQuery
orQSqlQueryModel
member functions that take a connection name argument, if you don’t pass a connection name, the default connection will be used. Creating a default connection is convenient when your application only requires one database connection.Note the difference between creating a connection and opening it. Creating a connection involves creating an instance of class
QSqlDatabase
. The connection is not usable until it is opened. The following snippet shows how to create a default connection and then open it:db = QSqlDatabase.addDatabase("QMYSQL") db.setHostName("bigblue") db.setDatabaseName("flightdb") db.setUserName("acarlson") db.setPassword("1uTbSbAs") ok = db.open()The first line creates the connection object, and the last line opens it for use. In between, we initialize some connection information, including the
database name
, thehost name
, theuser name
, and thepassword
. In this case, we are connecting to the MySQL databaseflightdb
on the hostbigblue
. The"QMYSQL"
argument toaddDatabase()
specifies the type of database driver to use for the connection. The set of database drivers included with Qt are shown in the table of supported database drivers .The connection in the snippet will be the default connection, because we don’t pass the second argument to
addDatabase()
, which is the connection name. For example, here we establish two MySQL database connections named"first"
and"second"
:firstDB = QSqlDatabase.addDatabase("QMYSQL", "first") secondDB = QSqlDatabase.addDatabase("QMYSQL", "second")After these connections have been initialized,
open()
for each one to establish the live connections. If theopen()
fails, it returnsfalse
. In that case, calllastError()
to get error information.Once a connection is established, we can call the static function
database()
from anywhere with a connection name to get a pointer to that database connection. If we don’t pass a connection name, it will return the default connection. For example:defaultDB = QSqlDatabase.database() firstDB = QSqlDatabase.database("first") secondDB = QSqlDatabase.database("second")To remove a database connection, first close the database using
close()
, then remove it using the static methodremoveDatabase()
.
© 2022 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation. Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.