QTableview data disappear..

[SGaist]

Hi,

Are you reseting the database connection ?

[TheCipo76]

@SGaist no but i have found in "Application Output":

QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work.
QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.

i've put DB declaration and DB.close() within brakets, than out of brakets, called:

QSqlDatabase::removeDatabase("QMYSQL");

but warning still remain..

Note that i can't use:

QSqlDatabase db = QSqlDatabase::database("dbname"); --> give me this error: Driver not loaded

but i'm using

QSqlDatabase mDatabase = QSqlDatabase::addDatabase("dbname"); --> run correctly

[SGaist]

Can you show exactly how you are handling QSqlDatabase in your application ?

Because it looks like you are either keeping local objects of that type or adding and removing the connection in several different unsynchronised parts of your application.

[TheCipo76]

@SGaist this is a dialog who show data from DB in a QTableView

#include "statoordini.h"
#include "ui_statoordini.h"
#include "QtSql"
#include "QtDebug"
//#include <QSqlTableModel>
#include <QSqlError>
#include <QMessageBox>


StatoOrdini::StatoOrdini(QWidget *parent, const QString &Utente, const QString &Password) :
    QDialog(parent),
    ui(new Ui::StatoOrdini),
    Utente(Utente),
    Password(Password)
{
    ui->setupUi(this);

    //qputenv("QT_DEBUG_PLUGINS", QByteArray("1"));

    {
        QSqlDatabase mDatabase = QSqlDatabase::addDatabase("QMYSQL");
        //localhost
        mDatabase.setHostName("192.168.1.250");
        //3306
        mDatabase.setPort(3307);
        mDatabase.setDatabaseName("MISSORA");
        mDatabase.setUserName(Utente);
        mDatabase.setPassword(Password);
        if (!mDatabase.open()) {
            QMessageBox::critical(this, "Error", mDatabase.lastError().text());
            return;
        };
    
        QSqlTableModel *mModel = new QSqlTableModel(this);
        mModel->setTable("ORDINI");
        mModel->select();
        ui->tableView->setModel(mModel);
        // Ordina al click su Header
        ui->tableView->setSortingEnabled(true);
        ui->tableView->horizontalHeader()->setSectionsClickable(1);
        // Ridimensiona Colonne tableView al Contenuto
        ui->tableView->horizontalHeader()->setSectionResizeMode(QHeaderView::ResizeToContents);
        ui->tableView->setColumnHidden(0,true);
        ui->tableView->setEditTriggers(QAbstractItemView::NoEditTriggers);
        ui->tableView->show();
    
        QString Name = mDatabase.connectionName();
        QMessageBox msg;
        msg.setText(Name);
        msg.exec();
        mDatabase.close();
    }
    QSqlDatabase::removeDatabase("QMYSQL");
}

StatoOrdini::~StatoOrdini()
{
    //qt_sql_default_connection;
    //QSqlDatabase::removeDatabase("QMYSQL");

    delete ui;
}

[Christian Ehrlicher]

@TheCipo76 said in QTableview data disappear..:

mDatabase.close();

How should this work? A QSqlModel needs access to the database at any time...

[TheCipo76]

@Christian-Ehrlicher as you see lower..

works!

[Christian Ehrlicher]

It works as long as the model does not need to refetch data from the database (e.g. due to scrolling or other circumstances).

[TheCipo76]

@Christian-Ehrlicher No, i'have tried to scroll and works fine.

This is only view of DB data.. no need to modify nothing in this dialog
and no need to reload data

[Christian Ehrlicher]

I'm giving up... would you please at least try to not to close the database and see if your problem goes away?

[TheCipo76]

@Christian-Ehrlicher Yes, i have putted "//" before close database instruction

//mDatabase.close();

but warning still remain..

[SGaist]

Are you calling QSqlDatabase::addDatabase("QMYSQL"); in several places in your application ?

[TheCipo76]

@SGaist Yes, in every dialog who need to connect to database..

but in every dialog call

ordforauto::~ordforauto()
{
    if (aDatabase.open()) {
        aDatabase.close();
    }
QSqlDatabase::removeDatabase("QMYSQL");
    delete ui;
}

in the code or at least in the unload istructions as you see

[Christian Ehrlicher]

http://doc.qt.io/qt-5/qsqlquery.html#details

Warning: You must load the SQL driver and open the connection before a QSqlQuery is created. Also, the connection must remain open while the query exists; otherwise, the behavior of QSqlQuery is undefined.

[SGaist]

Why are you doing it like that ? There's no need to nuke and recreate the connection each time.

If you really want to do it like that, then you should create a connection with a different name in each of your dialog.

Because currently, you are manipulating the default connection from several places in a wrong manner.

[TheCipo76]

@SGaist ok, i create the connection in the main window
and then only open/close database tables in every dialog?

is it right?

[TheCipo76]

@Christian-Ehrlicher i will check all dialogs.. but i think that is what i've done..

[jsulm]

@TheCipo76 As shown here: http://doc.qt.io/qt-5/qsqldatabase.html
Create and open db connection:

QSqlDatabase db = QSqlDatabase::addDatabase("QPSQL");
db.setHostName("acidalia");
db.setDatabaseName("customdb");
db.setUserName("mojito");
db.setPassword("J0a1m8");
bool ok = db.open();

When you need the connection just get it:

QSqlDatabase db = QSqlDatabase::database();

No need to open and close it all the time.

[TheCipo76]

@jsulm Ok, i've modify all my project and all works ok!

Thanks to all for help!