QSqlQuery problem

[MarkoSan]

Hi to all!

Here is the code:

QString queryString("SELECT * from merchandize WHERE GrupaIdentificationNumber=%1;");
    //QString queryString("SELECT * from merchandize WHERE GrupaIdentificationNumber=2;");    // test
    queryString=queryString.arg(groupId);
    qDebug() << "Query: " << queryString;    // debug
 
    QSqlQuery query(queryString);    // sets up query from query string
    removeAllMerchandize();    // removes all items
    m_iImageCounter=0;    // inits counter
    //query.exec(queryString);    // executes query string
    while (query.next())
    {
                 .....
    }

QString queryString("SELECT * from merchandize WHERE GrupaIdentificationNumber=%1;");
    //QString queryString("SELECT * from merchandize WHERE GrupaIdentificationNumber=2;");    // test
    queryString=queryString.arg(groupId);
    qDebug() << "Query: " << queryString;    // debug
    
    QSqlQuery query(queryString);    // sets up query from query string
    removeAllMerchandize();    // removes all items
    m_iImageCounter=0;    // inits counter
    //query.exec(queryString);    // executes query string
    while (query.next())
    {
                 .....
    }

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As you can see, I've debugged created query and it is ok. But why the program flow skips while loop. The database is filled and the application is connected to it as it must be. I thought there is something wrong with query itself, but as I copied quey, which was produces with qDebug() and pasted it into mysql by hand, I got right results. Can someone help me please?

[jacek]

What does QSqlQuery::isActive() return just before the loop?

[MarkoSan]

God damn, I've recoded the code using isActive like that:

void CMerchandizeBrowser::fillMerchandize(int groupId)
{
    qDebug() << "Entered CMerchandizeBrowser::fillMerchandize ...";    // debug
    // sets up query string
    QString queryString("SELECT * from merchandize WHERE GrupaIdentificationNumber=%1;");
    //QString queryString("SELECT * from merchandize WHERE GrupaIdentificationNumber=2;");    // test
    queryString=queryString.arg(groupId);
    qDebug() << "Query: " << queryString;    // debug
 
    QSqlQuery query(queryString);    // sets up query from query string
    removeAllMerchandize();    // removes all items
    m_iImageCounter=0;    // inits counter
    //query.exec(queryString);    // executes query string
    // WARNING: Are we connected to database????
    if (query.isActive())
    {
        while (query.next())
        {
            /*
            if (groupId==query.value(iMerchandizeFieldGROUPID).toInt())
            {
            */
                QImage img(query.value(iMerchandizeFieldPICPATH).toString());    // fetches image from filename
 
                tEmbeddImagesResult result=embeddedPicPath(img, query.value(iMerchandizeFieldPICPATH).toString());    // embedd pic path into pic
                if (result!=resFailue)
                {
                    img=img.convertToFormat(QImage::Format_ARGB32_Premultiplied);
                }
                //addMerchandize(query.value(iMerchandizeFieldPICPATH).toString());    // adds merchandize pics
                setSlideCount(m_iImageCounter+1);
                setSlide(m_iImageCounter, img);
                m_iImageCounter++;
            //}
        }    // while
    };
    m_iSelected=m_iImageCounter / 2;    // sets selected pic
 
    //update();    // updates window
    qDebug() << "m_iImageCounter: " << m_iImageCounter;    // debug
    qDebug() << "m_iSelected: " << m_iSelected;    // debug
    qDebug() << "Exiting CMerchandizeBrowser::fillMerchandize ...";    // debug
}

void CMerchandizeBrowser::fillMerchandize(int groupId)
{
    qDebug() << "Entered CMerchandizeBrowser::fillMerchandize ...";    // debug
    // sets up query string
    QString queryString("SELECT * from merchandize WHERE GrupaIdentificationNumber=%1;");
    //QString queryString("SELECT * from merchandize WHERE GrupaIdentificationNumber=2;");    // test
    queryString=queryString.arg(groupId);
    qDebug() << "Query: " << queryString;    // debug
    
    QSqlQuery query(queryString);    // sets up query from query string
    removeAllMerchandize();    // removes all items
    m_iImageCounter=0;    // inits counter
    //query.exec(queryString);    // executes query string
    // WARNING: Are we connected to database????
    if (query.isActive())
    {
        while (query.next())
        {
            /*
            if (groupId==query.value(iMerchandizeFieldGROUPID).toInt())
            {
            */
                QImage img(query.value(iMerchandizeFieldPICPATH).toString());    // fetches image from filename
                
                tEmbeddImagesResult result=embeddedPicPath(img, query.value(iMerchandizeFieldPICPATH).toString());    // embedd pic path into pic
                if (result!=resFailue)
                {
                    img=img.convertToFormat(QImage::Format_ARGB32_Premultiplied);
                }
                //addMerchandize(query.value(iMerchandizeFieldPICPATH).toString());    // adds merchandize pics
                setSlideCount(m_iImageCounter+1);
                setSlide(m_iImageCounter, img);
                m_iImageCounter++;
            //}
        }    // while
    };
    m_iSelected=m_iImageCounter / 2;    // sets selected pic

    //update();    // updates window
    qDebug() << "m_iImageCounter: " << m_iImageCounter;    // debug
    qDebug() << "m_iSelected: " << m_iSelected;    // debug
    qDebug() << "Exiting CMerchandizeBrowser::fillMerchandize ...";    // debug
}

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and isActive under if skips while loop. Thas means I am not connected to database??

[jacek]

Thas means I am not connected to database??

Not necessarily. What does QSqlQuery::lastError() return?

[MarkoSan]

God damn, the line

qDebug() << query.lastError().text();    // debug

qDebug() << query.lastError().text();    // debug

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returns

warning: "No database selected QMYSQL: Unable to execute query"

warning: "No database selected QMYSQL: Unable to execute query"

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. Jacek, thanks for hints, but clear this up for me please. How is it possible that in the same object and in other method, one time the database is active and the second time, like in this problem, it goes offline. Is there any timeout setting for MySQL database???

[jacek]

What happens in removeAllMerchandize()?

[MarkoSan]

Here is code, nothing special:

void CMerchandizeBrowser::removeAllMerchandize()
{
    qDebug() << "Entered CMerchandizeBrowser::removeAllMerchandize ...";    // debug
//    qDebug() << "Number of pics: " << m_ImagesList.count();
//    for(qint16 iIndex=0; iIndex<m_ImagesList.count(); iIndex++)
//    {
//        m_ImagesList.removeAt(iIndex);    // removes item
//    }
    //clear();    // clear slides of all images
    d->slideImages.clear();    // clears intertnal pic presentation
    //update();    // updates screen
    qDebug() << "Exiting CMerchandizeBrowser::removeAllMerchandize ...";    // debug
}

void CMerchandizeBrowser::removeAllMerchandize()
{
    qDebug() << "Entered CMerchandizeBrowser::removeAllMerchandize ...";    // debug
//    qDebug() << "Number of pics: " << m_ImagesList.count();
//    for(qint16 iIndex=0; iIndex<m_ImagesList.count(); iIndex++)
//    {
//        m_ImagesList.removeAt(iIndex);    // removes item
//    }
    //clear();    // clear slides of all images
    d->slideImages.clear();    // clears intertnal pic presentation
    //update();    // updates screen
    qDebug() << "Exiting CMerchandizeBrowser::removeAllMerchandize ...";    // debug
}

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And d is private class under CMerchandizeBrowser. Let me comment it and then see what happens.

[jacek]

How do you connect to the database? Do you use a named connection?

[MarkoSan]

I've coded database singleton class with your help, I think, a while ago and I am reusing it now in this application. Do you need a code?

[jacek]

No, I just want to know the line with addDatabase().

[MarkoSan]

Ok, here is the whole constructor of my CDatabaseFoundation class:

CDatabaseFoundation::CDatabaseFoundation(QString db_type, QString db_host,
                                         QString db_name, QString db_username,
                                         QString db_password): QObject()
{
  // sets up database paramaters
  m_Database=QSqlDatabase::addDatabase(db_type);
  m_Database.setHostName(db_host);
  m_Database.setUserName(db_username);
  m_Database.setPassword(db_password);
 
  // tries to connect to database
  m_bConnectionEstablished=m_Database.open();
  if(!m_bConnectionEstablished)
    qFatal("Failed to connect to database. Aborting.");
  //create database + tables if they don't exists yet
  //CreateDatabaseAndTables();
 
  //call seletedDatabase statement here because you're sure the the database exists
  m_Database.setDatabaseName(db_name);
 
 
/*
  m_pModel=new QSqlRelationalTableModel(this);
  Q_CHECK_PTR(m_pModel);
  //all changes will be cached in the model until either submitAll() or revertAll() is called
  m_pModel->setEditStrategy(QSqlTableModel::OnManualSubmit);
*/
  //addRelations(m_pModel);
 
}

CDatabaseFoundation::CDatabaseFoundation(QString db_type, QString db_host,
                                         QString db_name, QString db_username,
                                         QString db_password): QObject()
{
  // sets up database paramaters
  m_Database=QSqlDatabase::addDatabase(db_type);
  m_Database.setHostName(db_host);
  m_Database.setUserName(db_username);
  m_Database.setPassword(db_password);

  // tries to connect to database
  m_bConnectionEstablished=m_Database.open();
  if(!m_bConnectionEstablished)
    qFatal("Failed to connect to database. Aborting.");
  //create database + tables if they don't exists yet
  //CreateDatabaseAndTables();

  //call seletedDatabase statement here because you're sure the the database exists
  m_Database.setDatabaseName(db_name);

    
/*
  m_pModel=new QSqlRelationalTableModel(this);
  Q_CHECK_PTR(m_pModel);
  //all changes will be cached in the model until either submitAll() or revertAll() is called
  m_pModel->setEditStrategy(QSqlTableModel::OnManualSubmit);
*/
  //addRelations(m_pModel);

}

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[jacek]

// tries to connect to database
m_bConnectionEstablished=m_Database.open();
if(!m_bConnectionEstablished)
qFatal("Failed to connect to database. Aborting.");
//create database + tables if they don't exists yet
//CreateDatabaseAndTables();

//call seletedDatabase statement here because you're sure the the database exists
m_Database.setDatabaseName(db_name);

As the setDatabaseName() docs say: "This must be done before the connection is opened or it has no effect;". Put that line before the call to open().

[MarkoSan]

Ok, jacek, now query works fine. But please tell me, how is it possible that the SAME CODE worked before?????

[jacek]

how is it possible that the SAME CODE worked before?????

Yesterday was the 13th.

[MarkoSan]

Hmm, you can mock at me as much as you want, but in the same object other method works without problem, I tried it now. I have to solve this mistery, anyway, jacek, thank you very very much for your guidance.