Sqlite connection QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.

[SherifOmran]

Hello Gurus,

I am trying to fetch data from an SQLite database, it works fine, however when I try to call the function again it works but with an debug message

QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.

here is my code, do I close the connection correctly? thanks

@QSqlQuery MainForm::QuerydB(QString Query, QString dataBaseFile)
{
//QSqlQuery result;
//QString dbname;

database = new QSqlDatabase();
//set database driver to QSQLITE
*database = QSqlDatabase::addDatabase("QSQLITE");
database->setDatabaseName(dataBaseFile);
qDebug() << dataBaseFile;

if(!database->open())
{
    QMessageBox::warning(0,"Error","Couldn't open setting database");
    //qApp->setProperty("DatabaseOpen","ERROR");
}


 // read data
 QSqlQuery result (Query, *database);

//close database;
 QString connname = database->connectionName();


 database->close();
 database->removeDatabase(dataBaseFile);
 delete database;

 return result;

}
@

[Neutron Stein]

I think you have to call QSqlDatabase::addDatabase("QSQLITE"); once in your program

[SherifOmran]

But how can I then make it inform of a function?

[franku]

You may want to look "here":http://qt-project.org/forums/viewthread/18722/.

[Neutron Stein]

you just have to call it in the ctor of you class i think

[franku]

Normally you don't need to open the database connection more than once within your application. You also want to look at the sample code "here":http://doc.qt.nokia.com/4.7-snapshot/qsqldatabase.html#details.

Since each database connection will only have a single instance within the whole application you are able to access it via QSqlDatabase::connection().

I would suggest that you have three static functions in your MainForm. One that opens the database connection, one the exectues a query and the third to close the database. The first and the third are called i.e. in the MainForm constructor/destructor, as Neutron Stern wrote, the second whenever you need a query.

Please read the mentioned documentation there you will find the needed help.

[zakarrrr]

For all people who looks for a good solution, this is what i found, tried and works fine:
(PS : I have an application, which has more then one project in it, means more then one sql-connection)

Call addDatabase() only once in your application (see second parameter, can be anything)

@QSqlDatabase::addDatabase("QSQLITE", "MyDBConnectionName");@

Do this first whenever you want to do some stuff with your DB

@if (QSqlDatabase::contains("MyDBConnectionName"))
{
...e.g. query@

Now you must get an instance to db-object

@QSqlDatabase sqlDatabase = QSqlDatabase::database("MyDBConnectionName");@

Add DB information to your query

@QSqlQuery query(QSqlDatabase::database("MyDBConnectionName"));@

[nasimChildOfDesert]

@zakarrrr

Hi
I have the sampe problem and I solve it by this command :
if (QSqlDatabase::contains("NameOfConnection"))
{
QSqlDatabase::removeDatabase("NameOfConnection");
return
}
QSqlDatabase::addDatabase("QSQLITE", "NameOfConnection");
I hope it will beuseful.

[Christian Ehrlicher]

Your call to removeDatabase() is wrong - it takes the database connection name, not a filename: https://doc.qt.io/qt-6/qsqldatabase.html#removeDatabase

Also why do you call add/removeDatabase every time instead openening it once as described in the documentation?

[nasimChildOfDesert]

@Christian-Ehrlicher

thaks you for ur answer, we use it for our unit test.
I have another question abou threading may i ask u?

[Christian Ehrlicher]

@nasimChildOfDesert said in Sqlite connection QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.:

I have another question abou threading may i ask u?

You have to create a new db connection per thread. There are a lot of threads about this in the forum.

[nasimChildOfDesert]

@Christian-Ehrlicher
no imean do you know agood document about threading, mutex, socketprograming TCP
there are a lot of info on the net but most of them are not complete and no practical sample

[Christian Ehrlicher]

@nasimChildOfDesert said in Sqlite connection QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.:

threading, mutex, socketprograming TCP

You don't need threading for sockets/tcp when you use Qt. Seaching for 'Qt threading' or looking at the QTcpSocket documentation should be a good start.