QSqlDatabase connection issue

Cobra91151

Hi! I have the application witch requires connection to Database on the server. It all works well but after 4 minutes of inactivity of DB connection it displays errors.

I know the problem is with wait_timeout variable on DB server but I can't change it because I don't have permission to the server. On the server it has value of 240 seconds = 4 minutes.

I have added some check to execute query and it will check connection:

Code:

void Test::dbTest()
{
    QSqlQuery sqlQuery("some query", QSqlDatabase::database("ConnectionName"));
    sqlQuery.setForwardOnly(true);

    if (sqlQuery.size() > 0) {
       // Some action
    } else {
        int errorCode = sqlQuery.lastError().number();

        if (errorCode == 2013) {
            QSqlDatabase::database("ConnectionName").open(); // opens DB connection
            dbTest(); // runs recursively
        } else {
            qDebug() << sqlQuery.lastError().text();
        }
    }
}

It fixes such situation but I need to add such check for all functions that works with DB. But what if I can omit such check and everywhere just run QSqlDatabase::open() before query? What will happen when connection is still alive and QSqlDatabase::open() function will run again, it will create another connection or use existing? Thanks.

SGaist

Hi,

What about using a heartbeat on that connection ?

Cobra91151

@SGaist

Yes, it also will work. But I have checked QSqlDatabase::open() solution on WAMP and it creates only 1 connection to DB. Thanks.

SGaist

You should take a look at the QSqlDatabase::setConnectOptions and the specifics for MySQL. You could fine tune the timeout for your server.

Cobra91151

@SGaist

I have added setConnectOptions("MYSQL_OPT_RECONNECT=TRUE"); and now it automatically reconnects. Thanks.