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QSQlQuery::exec: database not open

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  • O Omar Alkersh

    Hello,

    So I have been receiving this error while running the following code

    void MainWindow::on_serachBox_textEdited(const QString& arg1) {
      // TODO: fix this
      // databse::exec: databse not open
      queryModel.setQuery("SELECT * FROM " + ui->comboBox->currentText() +
                              " WHERE " +
                              handler->getMainField(ui->comboBox->currentText()) +
                              " LIKE \'%" + arg1 + "%\'",
                          handler->getDB());
      qDebug() << queryModel.lastError();
      qDebug() << queryModel.query().lastQuery();
      ui->dataOutput->setModel(&queryModel);
    }
    

    This method runs when the text in line edit changed. I tried doing db->open(); before running thequeryModel.setQuery(...); but got no different result.
    What is really frustrating is when I run the following code, it runs without an issue:

    void MainWindow::updateQuery() {
      handler->open();
      queryModel.setQuery("SELECT * FROM " + ui->comboBox->currentText() +
                          " WHERE 1");
      handler->close();
      ui->dataOutput->setModel(&queryModel);
    }
    

    Can someone explain to me why I am getting this error and how I can fix it?

    Thank you.

    Application output:

    QSqlQuery::exec: database not open
    QSqlError("", "", "")
    "SELECT * FROM test1 WHERE testF_T LIKE '%3%'"
    

    PS.
    The query itself is fine, I checked it

    K Offline
    K Offline
    koahnig
    wrote on last edited by
    #2

    @Omar-Alkersh

    Hi and welcome to devnet forum

    There is not need to have a pointer for the db. You can simply open the default as it is shown in the detailed description here. However, you have to open the db prior to access.

    Vote the answer(s) that helped you to solve your issue(s)

    O 1 Reply Last reply
    1
    • SGaistS Offline
      SGaistS Offline
      SGaist
      Lifetime Qt Champion
      wrote on last edited by
      #3

      Hi and welcome to devnet,

      To add to @koahnig, what is that handler object ?

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

      O 1 Reply Last reply
      0
      • SGaistS SGaist

        Hi and welcome to devnet,

        To add to @koahnig, what is that handler object ?

        O Offline
        O Offline
        Omar Alkersh
        wrote on last edited by
        #4

        @SGaist just a normal object where I keep all my db related methods and object, QSqlQuery, QSqlDatabse etc.I

        1 Reply Last reply
        0
        • K koahnig

          @Omar-Alkersh

          Hi and welcome to devnet forum

          There is not need to have a pointer for the db. You can simply open the default as it is shown in the detailed description here. However, you have to open the db prior to access.

          O Offline
          O Offline
          Omar Alkersh
          wrote on last edited by
          #5

          @koahnig I open it at the constructor of the handler object, an object where I keep all the db related methods and vars, to keep things clean

          1 Reply Last reply
          0
          • O Omar Alkersh

            Hello,

            So I have been receiving this error while running the following code

            void MainWindow::on_serachBox_textEdited(const QString& arg1) {
              // TODO: fix this
              // databse::exec: databse not open
              queryModel.setQuery("SELECT * FROM " + ui->comboBox->currentText() +
                                      " WHERE " +
                                      handler->getMainField(ui->comboBox->currentText()) +
                                      " LIKE \'%" + arg1 + "%\'",
                                  handler->getDB());
              qDebug() << queryModel.lastError();
              qDebug() << queryModel.query().lastQuery();
              ui->dataOutput->setModel(&queryModel);
            }
            

            This method runs when the text in line edit changed. I tried doing db->open(); before running thequeryModel.setQuery(...); but got no different result.
            What is really frustrating is when I run the following code, it runs without an issue:

            void MainWindow::updateQuery() {
              handler->open();
              queryModel.setQuery("SELECT * FROM " + ui->comboBox->currentText() +
                                  " WHERE 1");
              handler->close();
              ui->dataOutput->setModel(&queryModel);
            }
            

            Can someone explain to me why I am getting this error and how I can fix it?

            Thank you.

            Application output:

            QSqlQuery::exec: database not open
            QSqlError("", "", "")
            "SELECT * FROM test1 WHERE testF_T LIKE '%3%'"
            

            PS.
            The query itself is fine, I checked it

            J.HilkJ Offline
            J.HilkJ Offline
            J.Hilk
            Moderators
            wrote on last edited by
            #6

            @Omar-Alkersh

            the only difference between the 2 code examples you posted is, that in one you pass the database to the queryModel.

            You said you tested it, and it did not work, what exactly is the result when you would change the function to this:

            void MainWindow::on_serachBox_textEdited(const QString& arg1) {
            
            handler->open();
              queryModel.setQuery("SELECT * FROM " + ui->comboBox->currentText() +
                                      " WHERE " +
                                      handler->getMainField(ui->comboBox->currentText()) +
                                      " LIKE \'%" + arg1 + "%\'");
              qDebug() << queryModel.lastError();
              qDebug() << queryModel.query().lastQuery();
              handler->close();
              ui->dataOutput->setModel(&queryModel);
            }
            

            I haven't used the QSqlQueryModel class myself yet, but are you supposed to to piece the query together like this!? Seems wrong.


            Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


            Q: What's that?
            A: It's blue light.
            Q: What does it do?
            A: It turns blue.

            O 1 Reply Last reply
            0
            • J.HilkJ J.Hilk

              @Omar-Alkersh

              the only difference between the 2 code examples you posted is, that in one you pass the database to the queryModel.

              You said you tested it, and it did not work, what exactly is the result when you would change the function to this:

              void MainWindow::on_serachBox_textEdited(const QString& arg1) {
              
              handler->open();
                queryModel.setQuery("SELECT * FROM " + ui->comboBox->currentText() +
                                        " WHERE " +
                                        handler->getMainField(ui->comboBox->currentText()) +
                                        " LIKE \'%" + arg1 + "%\'");
                qDebug() << queryModel.lastError();
                qDebug() << queryModel.query().lastQuery();
                handler->close();
                ui->dataOutput->setModel(&queryModel);
              }
              

              I haven't used the QSqlQueryModel class myself yet, but are you supposed to to piece the query together like this!? Seems wrong.

              O Offline
              O Offline
              Omar Alkersh
              wrote on last edited by Omar Alkersh
              #7

              @J.Hilk hello,
              The result is that I get the same meessge, QSqlQuery::exec: database not open, regardless whether I write handler->ope (); or not.
              The QTableView, which I use this model with, would stop displaying any table.

              Basically no difference.

              jsulmJ 1 Reply Last reply
              0
              • O Omar Alkersh

                @J.Hilk hello,
                The result is that I get the same meessge, QSqlQuery::exec: database not open, regardless whether I write handler->ope (); or not.
                The QTableView, which I use this model with, would stop displaying any table.

                Basically no difference.

                jsulmJ Offline
                jsulmJ Offline
                jsulm
                Lifetime Qt Champion
                wrote on last edited by
                #8

                @Omar-Alkersh Can you show the content of handler->open() ?

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

                O 1 Reply Last reply
                0
                • jsulmJ jsulm

                  @Omar-Alkersh Can you show the content of handler->open() ?

                  O Offline
                  O Offline
                  Omar Alkersh
                  wrote on last edited by
                  #9

                  @jsulm

                  
                  QSqlDatabase db; //initialised in constructor
                  
                  void BDHandler::open (){
                  db->open ();
                  }
                  
                  handler->close (); //same as open
                  
                  jsulmJ 1 Reply Last reply
                  0
                  • O Omar Alkersh

                    @jsulm

                    
                    QSqlDatabase db; //initialised in constructor
                    
                    void BDHandler::open (){
                    db->open ();
                    }
                    
                    handler->close (); //same as open
                    
                    jsulmJ Offline
                    jsulmJ Offline
                    jsulm
                    Lifetime Qt Champion
                    wrote on last edited by
                    #10

                    @Omar-Alkersh said in QSQlQuery::exec: database not open:

                    QSqlDatabase db;

                    If this is like this in the constructor then it is a local variable in the constructor and not related to the db pointer!
                    You also should check the return value of db->open () and print out the output of http://doc.qt.io/qt-4.8/qsqldatabase.html#lastError in case it returns false. Also you did not say how you set up your database.

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

                    O 1 Reply Last reply
                    0
                    • jsulmJ jsulm

                      @Omar-Alkersh said in QSQlQuery::exec: database not open:

                      QSqlDatabase db;

                      If this is like this in the constructor then it is a local variable in the constructor and not related to the db pointer!
                      You also should check the return value of db->open () and print out the output of http://doc.qt.io/qt-4.8/qsqldatabase.html#lastError in case it returns false. Also you did not say how you set up your database.

                      O Offline
                      O Offline
                      Omar Alkersh
                      wrote on last edited by
                      #11

                      @jsulm

                      Thanks for the suggestion but this is a global variable, it is just initialized in the constructor.

                      And this is how I set up my db

                      DBHandler::DBHandler(MainWindow* mWindow) {
                        // init vars
                        path = databaseloc.currentPath() + "/database";
                        TABLE_MAIN = "main_table";
                        COLUMN_ID = "_id";
                        COLUMN_MAIN_NAME = "main_name";
                      
                        // check if dir exits
                        QFileInfo fileInfo(path);
                        if (!fileInfo.exists()) {
                          if (databaseloc.mkpath(path)) {
                            mWindow->close();
                          }
                        }
                      
                        // db name and loc
                        path += "/" + dbName + ".db";
                      
                        // add db
                        db = QSqlDatabase::addDatabase("QSQLITE");
                        db.setDatabaseName(path);
                      
                        // open test, sets up query and creates mainTable if not exists
                        if (db.open()) {
                          query = QSqlQuery(db);
                          query.exec("CREATE TABLE IF NOT EXISTS " + TABLE_MAIN + "(" + COLUMN_ID +
                                     " INTEGER PRIMARY KEY AUTOINCREMENT, " + COLUMN_MAIN_NAME +
                                     " TEXT, mainField TEXT);");
                      
                        } else {
                          // stop programme from continueing
                          QMessageBox::StandardButton reply;
                      
                          reply = QMessageBox::warning(
                              mWindow, "Error",
                              "Was not able to open database file.\n" + db.lastError().text());
                      
                          if (reply == QMessageBox::Ok) {
                            // exits with error
                            exit(1);
                          }
                        }
                        db.close();
                      }
                      
                      
                      K 1 Reply Last reply
                      0
                      • O Omar Alkersh

                        @jsulm

                        Thanks for the suggestion but this is a global variable, it is just initialized in the constructor.

                        And this is how I set up my db

                        DBHandler::DBHandler(MainWindow* mWindow) {
                          // init vars
                          path = databaseloc.currentPath() + "/database";
                          TABLE_MAIN = "main_table";
                          COLUMN_ID = "_id";
                          COLUMN_MAIN_NAME = "main_name";
                        
                          // check if dir exits
                          QFileInfo fileInfo(path);
                          if (!fileInfo.exists()) {
                            if (databaseloc.mkpath(path)) {
                              mWindow->close();
                            }
                          }
                        
                          // db name and loc
                          path += "/" + dbName + ".db";
                        
                          // add db
                          db = QSqlDatabase::addDatabase("QSQLITE");
                          db.setDatabaseName(path);
                        
                          // open test, sets up query and creates mainTable if not exists
                          if (db.open()) {
                            query = QSqlQuery(db);
                            query.exec("CREATE TABLE IF NOT EXISTS " + TABLE_MAIN + "(" + COLUMN_ID +
                                       " INTEGER PRIMARY KEY AUTOINCREMENT, " + COLUMN_MAIN_NAME +
                                       " TEXT, mainField TEXT);");
                        
                          } else {
                            // stop programme from continueing
                            QMessageBox::StandardButton reply;
                        
                            reply = QMessageBox::warning(
                                mWindow, "Error",
                                "Was not able to open database file.\n" + db.lastError().text());
                        
                            if (reply == QMessageBox::Ok) {
                              // exits with error
                              exit(1);
                            }
                          }
                          db.close();
                        }
                        
                        
                        K Offline
                        K Offline
                        koahnig
                        wrote on last edited by
                        #12

                        @Omar-Alkersh

                        Did you notice the close at the end of your constructor?

                         }
                          db.close();
                        }
                        

                        I guess there is your problem.

                        Vote the answer(s) that helped you to solve your issue(s)

                        1 Reply Last reply
                        3
                        • SGaistS Offline
                          SGaistS Offline
                          SGaist
                          Lifetime Qt Champion
                          wrote on last edited by
                          #13

                          Hi,

                          To add to @koahnig, why are you opening and closing the database connection again and again ?

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

                          O 1 Reply Last reply
                          0
                          • SGaistS SGaist

                            Hi,

                            To add to @koahnig, why are you opening and closing the database connection again and again ?

                            O Offline
                            O Offline
                            Omar Alkersh
                            wrote on last edited by Omar Alkersh
                            #14

                            @SGaist Thank you good sir. It worked. I thought that I should always close the db to stop any memory leaks. I used to develop android and I used to always close it after me.

                            Solution was not to close the db. Obviously.

                            1 Reply Last reply
                            0
                            • SGaistS Offline
                              SGaistS Offline
                              SGaist
                              Lifetime Qt Champion
                              wrote on last edited by
                              #15

                              AFAIK, there's no known memory leaks in Qt's SQL drivers.

                              Don't get me wrong, there might be good reasons to only open a database connection when needed however this requires a bit more architecture to make it work correctly.

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

                              1 Reply Last reply
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