QMYSQL - Naming a connection makes drivers unavailable

[RyanR]

Hey guys,

I currently have an issue with QtSql/QSqlDatabase libraries with Qt C++ on Debian with Qt Creator 5.8.2 (Qt 5.11.3 GCC 32 bit); my latest industrial software engineering project requires multiple MySQL database connections on different threads. After some research, it seems that I need to name my database connections. However whenever I add a second argument to QSqlDatabase::addDatabase, the drivers become unavailable.

The following code works fine and I can verify on the SQL CLI that the data is being received correctly:

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
 
    db.setHostName("00.00.000.000");
    db.setDatabaseName("00000");
    db.setUserName("00000");
    db.setPassword("00000");
 
    bool dbOk = db.open();
 
    if(dbOk)
    {
        qDebug() << "Connected to Database.";
 
        QString queryData;
        queryData.sprintf("INSERT INTO `dev`.`logs` (`logid`, `timestamp`, `command`) VALUES (NULL, CURRENT_TIMESTAMP, 'Test')");
 
        qDebug() << "Output Query Data: " << queryData << ".";
 
        QSqlQuery query(queryData);
 
        if(!query.isActive())
        {
            qDebug() << "ERROR Error with database query! " << "Last Database Error: " << db.lastError() << ". Last Query Error: " << query.lastError() << ".";
 
        }
        else
        {
            qDebug() << "Query is good!";
        }
    }
 
    QString connection;
    connection = db.connectionName();
    db.close();
    db = QSqlDatabase();
    db.removeDatabase(connection);

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");

    db.setHostName("00.00.000.000");
    db.setDatabaseName("00000");
    db.setUserName("00000");
    db.setPassword("00000");

    bool dbOk = db.open();

    if(dbOk)
    {
        qDebug() << "Connected to Database.";

        QString queryData;
        queryData.sprintf("INSERT INTO `dev`.`logs` (`logid`, `timestamp`, `command`) VALUES (NULL, CURRENT_TIMESTAMP, 'Test')");

        qDebug() << "Output Query Data: " << queryData << ".";

        QSqlQuery query(queryData);

        if(!query.isActive())
        {
            qDebug() << "ERROR Error with database query! " << "Last Database Error: " << db.lastError() << ". Last Query Error: " << query.lastError() << ".";

        }
        else
        {
            qDebug() << "Query is good!";
        }
    }
    
    QString connection;
    connection = db.connectionName();
    db.close();
    db = QSqlDatabase();
    db.removeDatabase(connection);

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But when I change:

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");

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To:

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL", "MyConnName");

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL", "MyConnName");

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I get "ERROR Error with database query! Last Database Error: QSqlError("", "", "") . Last Query Error: QSqlError("", "Driver not loaded", "Driver not loaded") .". Does anyone have any idea as to why this is happening?

Any help would be greatly appreciated!

Thanks,
Ryan

[^NyAw^]

Hi,

In line 19 you are not passing the Database to the query, so it basically worked because you only had one database connection. It is using the default Database.

QSqlQuery query(queryData,db);

QSqlQuery query(queryData,db);

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[RyanR]

Legend, that's got it working!

Now every time I create a new thread I pass the thread ID as the database connection name, and I can have separate MySQL connections per thread.

Thanks very much for the help!