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Qt SQL Class

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  • SGaistS Offline
    SGaistS Offline
    SGaist
    Lifetime Qt Champion
    wrote on last edited by
    #17

    You did not check that the query ran successfully.

    Also, as you were already explained: do not keep a QSqlDatabase class variable. It's all explained in the class details.

    Also, since you are using an SQLite database, ensure that the path you use is correct. If not, a new empty database will be created. This is SQLite specific and not something under Qt control.

    Interested in AI ? www.idiap.ch
    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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    • SGaistS SGaist

      You did not check that the query ran successfully.

      Also, as you were already explained: do not keep a QSqlDatabase class variable. It's all explained in the class details.

      Also, since you are using an SQLite database, ensure that the path you use is correct. If not, a new empty database will be created. This is SQLite specific and not something under Qt control.

      K Offline
      K Offline
      Kris Revi
      wrote on last edited by
      #18

      @SGaist said in Qt SQL Class:

      Also, as you were already explained: do not keep a QSqlDatabase class variable. It's all explained in the class details.

      why do i see alot of examples online where people keep it in a class? is this a new thing that changed?

      jsulmJ 1 Reply Last reply
      0
      • K Kris Revi

        @SGaist said in Qt SQL Class:

        Also, as you were already explained: do not keep a QSqlDatabase class variable. It's all explained in the class details.

        why do i see alot of examples online where people keep it in a class? is this a new thing that changed?

        jsulmJ Offline
        jsulmJ Offline
        jsulm
        Lifetime Qt Champion
        wrote on last edited by
        #19

        @Kris-Revi said in Qt SQL Class:

        is this a new thing that changed?

        No. There are also bad examples out there.

        https://forum.qt.io/topic/113070/qt-code-of-conduct

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        • jsulmJ jsulm

          @Kris-Revi said in Qt SQL Class:

          is this a new thing that changed?

          No. There are also bad examples out there.

          K Offline
          K Offline
          Kris Revi
          wrote on last edited by
          #20

          @jsulm said in Qt SQL Class:

          No. There are also bad examples out there.

          but 90% off the examples all have it in a custom class :S how can ALL of them be bad

          jsulmJ 1 Reply Last reply
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          • K Kris Revi

            @jsulm said in Qt SQL Class:

            No. There are also bad examples out there.

            but 90% off the examples all have it in a custom class :S how can ALL of them be bad

            jsulmJ Offline
            jsulmJ Offline
            jsulm
            Lifetime Qt Champion
            wrote on last edited by
            #21

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

            https://forum.qt.io/topic/113070/qt-code-of-conduct

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            • jsulmJ 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...

              K Offline
              K Offline
              Kris Revi
              wrote on last edited by
              #22

              @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?

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              • SGaistS Offline
                SGaistS Offline
                SGaist
                Lifetime Qt Champion
                wrote on last edited by
                #23

                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.

                Interested in AI ? www.idiap.ch
                Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                • SGaistS 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.

                  K Offline
                  K Offline
                  Kris Revi
                  wrote on last edited by Kris Revi
                  #24

                  @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();
                      
                                  }
                      
                              }
                      
                          });
                      
                      }
                  
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                  • SGaistS Offline
                    SGaistS Offline
                    SGaist
                    Lifetime Qt Champion
                    wrote on last edited by
                    #25

                    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.

                    Interested in AI ? www.idiap.ch
                    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                    • SGaistS 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.

                      K Offline
                      K Offline
                      Kris Revi
                      wrote on last edited by Kris Revi
                      #26

                      @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

                      JonBJ 1 Reply Last reply
                      0
                      • K 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

                        JonBJ Offline
                        JonBJ Offline
                        JonB
                        wrote on last edited by JonB
                        #27

                        @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.

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                        • SGaistS Offline
                          SGaistS Offline
                          SGaist
                          Lifetime Qt Champion
                          wrote on last edited by
                          #28

                          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.

                          Interested in AI ? www.idiap.ch
                          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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