QSqlQuery exec blocking function

[reinki0013]

hi,

my problem is that the

QSqlQuery::exec()

QSqlQuery::exec()

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function is blocking my application when the network-connection is down.

i tried to set the flag

MYSQL_OPT_RECONNECT=1

MYSQL_OPT_RECONNECT=1

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with

QSqlQuery::setConnectOptions()

QSqlQuery::setConnectOptions()

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but this doesn`t help.

is there any workaround about this or what can i do to solve this problem?

kind regards,
reinki

[reinki0013]

Can anybody help me with my problem?

[Lykurg]

You can first check if the network connection is down. Or put all database interaction in a thread.

[reinki0013]

hey,

in my case it could be, that the network-connection is up (before the exec()) and during the exec() it could be down - so it blocks my application.
Before the exec() i watched with a thread if the network-connection is down - but during the exec() i don`t have any chance.

so what can i do?

---

Added after 24 minutes:

I`ve tried to build a QThread with my .exec():

Implementation in my QThread-Classe:

void cExecThread::run()
{
    msleep(500);
    QSqlDatabase db = m_Database;    
    db.exec(m_Query);
}

void cExecThread::run()
{
    msleep(500);
    QSqlDatabase db = m_Database;    
    db.exec(m_Query);
}

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In my class where I need this exec() I do it like this:

void cDatabase::RemoveBusNr(QString TableName, QString BusNr)
{
    if(db.isValid() && m_Connected)
    {
        QSqlQuery sql_query(db);
 
        QString query = "DELETE FROM `";
        query += TableName + "` WHERE `BusNr` = '";
        query += BusNr += "';";
 
        Exec(query);
        //sql_query.exec(query);
        CheckSqlError();
        //qDebug() << query;
    }
}

void cDatabase::RemoveBusNr(QString TableName, QString BusNr)
{
    if(db.isValid() && m_Connected)
    {
        QSqlQuery sql_query(db);

        QString query = "DELETE FROM `";
        query += TableName + "` WHERE `BusNr` = '";
        query += BusNr += "';";

        Exec(query);
        //sql_query.exec(query);
        CheckSqlError();
        //qDebug() << query;
    }
}

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And here is the implementation from my Exec()-Function:

void cDatabase::Exec(QString query)
{  
    execThread.m_Database = db;
    execThread.m_Query = query;
    execThread.start();
 
    int iCount = 0;
 
    while(execThread.isRunning())
    {
        if(iCount < 5000)
            iCount++;
        else
        {
            execThread.terminate();
 
            if(execThread.isFinished())
              qDebug() << "Thread finished";
 
        }
    }
}

void cDatabase::Exec(QString query)
{  
    execThread.m_Database = db;
    execThread.m_Query = query;
    execThread.start();

    int iCount = 0;

    while(execThread.isRunning())
    {
        if(iCount < 5000)
            iCount++;
        else
        {
            execThread.terminate();

            if(execThread.isFinished())
              qDebug() << "Thread finished";

        }
    }
}

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But this doesn`t work very well - it works wrong and delayed my programm.

[yeye_olive]

The whole point of using threads is to prevent your GUI thread to be frozen during the blocking exec() call, but your code busy waits for the worker thread to finish and terminates it brutally after a while. I suggest you use a higher-level alternative like QtConcurrent::run() instead, it will be a lot easier. Read the docs and examples on QtConcurrent first.

[Lykurg]

And also read about SQL-Injections!!! Use QSqlQuery::prepare()... Further do not share a database connection between threads because they can crash.