Qt SQL Class

[jsulm]

@Kris-Revi What examples do you have in mind?
And did you read the documentation you where pointed to? There it is clearly stated...

[Kris Revi]

@jsulm said in Qt SQL Class:

And did you read the documentation you where pointed to? There it is clearly stated...

reading now! so for login i should use QSqlQueryModel since it is read-only and not QSqlQuery am i understanding that correctly?

[SGaist]

No, you should:

• properly handle the QSqlDatabase object
• properly check that all your queries are successful

QSqlQuery will not modify your database unless you write such a statement.

[Kris Revi]

@SGaist said in Qt SQL Class:

QSqlQuery will not modify your database unless you write such a statement.

Sooo THIS works it throws error if it cannot find username and password and i get "logged in" when i provide the correct username and password... am i still doing ANYTHING wrong?

    connect(ui->pushButtonLogin, &QPushButton::clicked, [=]()
    
        {        
    
            QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    
            //db.setHostName("acidalia");
    
            db.setDatabaseName("C:/crap/db.sqlite");
    
            //db.setDatabaseName("customdb");
    
            //db.setUserName("mojito");
    
            //db.setPassword("J0a1m8");
    
            bool ok = db.open();
    
            if(ok)
    
            {
    
                qInfo() << "Database Connected!";
    
    
    
                QSqlQuery query;
    
                query.prepare(QString("SELECT * FROM users WHERE username = (:username) AND password = (:password) "));
    
                query.bindValue(":username", ui->usernameText->text());
    
                query.bindValue(":password", ui->passwordText->text());
    
                query.exec();
    
    
    
                if (query.next())
    
                {
    
                    m_username = ui->usernameText->text();
    
                    m_password = ui->passwordText->text();
    
                    m_isloggedin = true;
    
                    ui->errorLabel->setVisible(false);
    
                    ui->stackedWidget->setCurrentIndex(1);
    
                    QString name = query.value(1).toString();
    
                    qDebug() << name << "is logged in";
    
                }
    
                else
    
                {
    
                    m_username = "";
    
                    m_password = "";
    
                    m_isloggedin = false;
    
                    ui->errorLabel->setVisible(true);
    
                    ui->errorLabel->setText("Invalid username or password.");
    
                    qWarning() << "Query Error : " << query.lastError();
    
                }
    
            }
    
        });
    
    }

[SGaist]

Yes, you are recreating your connection every time this slot is called which is not needed. And you are likely getting a warning while running your application and clicking your pushButtonLogin button multiple times.

[Kris Revi]

@SGaist said in Qt SQL Class:

Yes, you are recreating your connection every time this slot is called which is not needed. And you are likely getting a warning while running your application and clicking your pushButtonLogin button multiple times.

moved QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE"); to the mainwindow.h file

[JonB]

@Kris-Revi
I'm afraid that is not a good idea! Assuming you mean it is now a member variable, that is what @SGaist/Qt are asking you not to do. Have another careful read through https://doc.qt.io/qt-6/qsqldatabase.html#details, particularly the red box:

Warning: It is highly recommended that you do not keep a copy of the QSqlDatabase around as a member of a class, as this will prevent the instance from being correctly cleaned up on shutdown. If you need to access an existing QSqlDatabase, it should be accessed with database(). If you chose to have a QSqlDatabase member variable, this needs to be deleted before the QCoreApplication instance is deleted, otherwise it may lead to undefined behavior.

Do the addDatabase() and open stuff somewhere early in code, don't save the QSqlDatabase db.

You don't need the member variable because you can use QSqlDatabase db = QSqlDatabase::database(); just as a local variable whenever you need to access the default connection.

[SGaist]

If you are only using the default connection, then there's no need to do anything special beside the setup since it's the connection that will be used when no others have been created.

No need to over-engineer that stuff.
The usual main reason to retrieve the default connection is for example when you want to change credentials or in your case change the path to the database file.