Query on MS Access DB cause crash

[Bruschetta]

Hello guys,
i'm trying to make a query on an application that is connected with a .mdb file.
In one of my dialogs i can populate a tableView with no problem and then close the dialog without any problems, let's say i'm reading records from the DB table "PEOPLE".
In the same dialog i have a form to add rows to PEOPLE table. I can add 1-n° rows but when i close the dialog the application crashes EVERY time.
Things like this never happened to me when i was using SQLite DB.

Let me post some of my code, maybe you can help...

This is the way i'm doing my connection with the ACCESS .mdb file

bool connectionOpen(){
        static const QString path = PATH;
        mydb = QSqlDatabase::addDatabase("QODBC", "Contact");
        QString params="Driver={Microsoft Access Driver (*.mdb, *.accdb)};DSN='';DBQ="+ path;
        mydb.setDatabaseName(params);
 
        if (!mydb.open())
        {
            qDebug() << "Error: connection with database fail";
            qDebug() << mydb.lastError().text();
            return false;
        }
        else
        {
            qDebug() << "Database: connection ok";
            return true;
        }
        return true;

bool connectionOpen(){
        static const QString path = PATH;
        mydb = QSqlDatabase::addDatabase("QODBC", "Contact");
        QString params="Driver={Microsoft Access Driver (*.mdb, *.accdb)};DSN='';DBQ="+ path;
        mydb.setDatabaseName(params);

        if (!mydb.open())
        {
            qDebug() << "Error: connection with database fail";
            qDebug() << mydb.lastError().text();
            return false;
        }
        else
        {
            qDebug() << "Database: connection ok";
            return true;
        }
        return true;

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This is showing the rows and is working as intended

void class::on_pushButton_refreshListP_clicked()
{
 
 
    QSqlDatabase db = QSqlDatabase::database("Contact");
 
    if (db.isOpen())
    {
        QSqlTableModel *model = new QSqlTableModel(this,db);
        model->setTable("class");
        model->setEditStrategy(QSqlTableModel::OnFieldChange);
 
        model->setHeaderData(0, Qt::Horizontal, tr("a"));
        model->setHeaderData(1, Qt::Horizontal, tr("b"));
        model->setHeaderData(2, Qt::Horizontal, tr("c"));
        model->select();
 
        ui->tableView->setModel(model);
}

void class::on_pushButton_refreshListP_clicked()
{
   

    QSqlDatabase db = QSqlDatabase::database("Contact");
  
    if (db.isOpen())
    {
        QSqlTableModel *model = new QSqlTableModel(this,db);
        model->setTable("class");
        model->setEditStrategy(QSqlTableModel::OnFieldChange);

        model->setHeaderData(0, Qt::Horizontal, tr("a"));
        model->setHeaderData(1, Qt::Horizontal, tr("b"));
        model->setHeaderData(2, Qt::Horizontal, tr("c"));
        model->select();

        ui->tableView->setModel(model);
}

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This is the part of code that is working till i close the dialog... Than the application crashes

if (db.isOpen())
    {
        QSqlQuery query(db);
       // query.setForwardOnly(true);
        query.prepare("INSERT INTO class(a, b, c)    "
                      "   VALUES ( :a,:b, :c)");
 
 
        query.bindValue(":a", a);
        query.bindValue(":b", b);
        query.bindValue(":c", c);
 
 
        if(query.exec())
        {
            qDebug() << "exec";
            QTimer::singleShot(0, this, SLOT(on_pushButton_refreshListP_clicked()));
        }

if (db.isOpen())
    {
        QSqlQuery query(db);
       // query.setForwardOnly(true);
        query.prepare("INSERT INTO class(a, b, c)    "
                      "   VALUES ( :a,:b, :c)");


        query.bindValue(":a", a);
        query.bindValue(":b", b);
        query.bindValue(":c", c);
    

        if(query.exec())
        {
            qDebug() << "exec";
            QTimer::singleShot(0, this, SLOT(on_pushButton_refreshListP_clicked()));
        }

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someone can tell me what im'm doing wrong? I'm missing some configuration for the MS ACCESS?

Thank you for your time and answers

[d_stranz]

In line 5 of the second piece of code, you are defining a local variable named "db". In line 1 of the third piece of code, you are using another variable named "db". If the one in the third piece of code is a member variable of your class (which can't be named "class" - that's a reserved word in C++ and not legal to use as a class name), then the one in the second piece of code is hiding that one, and therefore the one in the third piece of code is probably never initialized.