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Thread: QMYSQL - Naming a connection makes drivers unavailable

  1. #1
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    Question QMYSQL - Naming a connection makes drivers unavailable

    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:
    Qt Code:
    1. QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
    2.  
    3. db.setHostName("00.00.000.000");
    4. db.setDatabaseName("00000");
    5. db.setUserName("00000");
    6. db.setPassword("00000");
    7.  
    8. bool dbOk = db.open();
    9.  
    10. if(dbOk)
    11. {
    12. qDebug() << "Connected to Database.";
    13.  
    14. QString queryData;
    15. queryData.sprintf("INSERT INTO `dev`.`logs` (`logid`, `timestamp`, `command`) VALUES (NULL, CURRENT_TIMESTAMP, 'Test')");
    16.  
    17. qDebug() << "Output Query Data: " << queryData << ".";
    18.  
    19. QSqlQuery query(queryData);
    20.  
    21. if(!query.isActive())
    22. {
    23. qDebug() << "ERROR Error with database query! " << "Last Database Error: " << db.lastError() << ". Last Query Error: " << query.lastError() << ".";
    24.  
    25. }
    26. else
    27. {
    28. qDebug() << "Query is good!";
    29. }
    30. }
    31.  
    32. QString connection;
    33. connection = db.connectionName();
    34. db.close();
    35. db = QSqlDatabase();
    36. db.removeDatabase(connection);
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    But when I change:

    Qt Code:
    1. QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
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    To:

    Qt Code:
    1. 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

  2. #2
    Join Date
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    Default Re: QMYSQL - Naming a connection makes drivers unavailable

    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.

    Qt Code:
    1. QSqlQuery query(queryData,db);
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    Òscar Llarch i Galán

  3. The following user says thank you to ^NyAw^ for this useful post:

    RyanR (16th September 2020)

  4. #3
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    Default Re: QMYSQL - Naming a connection makes drivers unavailable

    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!

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