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Mysql table locking error

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  • KutyusK Kutyus

    @jsulm LastError().text() is empty.

    JonBJ Offline
    JonBJ Offline
    JonB
    wrote on last edited by JonB
    #4

    @Kutyus
    Probably show your code so we can see (including where "unlock tables" gives a false result but no lastError() information). Also read through e.g. https://dev.mysql.com/doc/refman/8.0/en/lock-tables.html#table-lock-release to make sure you are complying with unlock requirements/behaviour.

    KutyusK 1 Reply Last reply
    0
    • JonBJ JonB

      @Kutyus
      Probably show your code so we can see (including where "unlock tables" gives a false result but no lastError() information). Also read through e.g. https://dev.mysql.com/doc/refman/8.0/en/lock-tables.html#table-lock-release to make sure you are complying with unlock requirements/behaviour.

      KutyusK Offline
      KutyusK Offline
      Kutyus
      wrote on last edited by
      #5

      @JonB
      If I run a QSqlQuery::clear() before the "unlock tables", it is working, but I do not know why?

      JonBJ 1 Reply Last reply
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      • KutyusK Kutyus

        @JonB
        If I run a QSqlQuery::clear() before the "unlock tables", it is working, but I do not know why?

        JonBJ Offline
        JonBJ Offline
        JonB
        wrote on last edited by JonB
        #6

        @Kutyus
        This is purely a guess.

        While you have some existing SQL query around/open which has a LOCK TABLES or is in a transaction with such, locks can't be released? You need to finish reading/close/terminate/clear the query to release the result set/previous query so that unlocking can proceed?

        KutyusK 1 Reply Last reply
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        • JonBJ JonB

          @Kutyus
          This is purely a guess.

          While you have some existing SQL query around/open which has a LOCK TABLES or is in a transaction with such, locks can't be released? You need to finish reading/close/terminate/clear the query to release the result set/previous query so that unlocking can proceed?

          KutyusK Offline
          KutyusK Offline
          Kutyus
          wrote on last edited by Kutyus
          #7

          @JonB
          Yes that is how it works.

          If I comment out the query between lock and unlock, it works that way.

          1 Reply Last reply
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          • SGaistS Offline
            SGaistS Offline
            SGaist
            Lifetime Qt Champion
            wrote on last edited by
            #8

            Hi,

            Can you show the code your using ?

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

            KutyusK 1 Reply Last reply
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            • Christian EhrlicherC Online
              Christian EhrlicherC Online
              Christian Ehrlicher
              Lifetime Qt Champion
              wrote on last edited by
              #9

              @JonB said in Mysql table locking error:

              LOCK TABLES

              Why do you need it at all?

              Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
              Visit the Qt Academy at https://academy.qt.io/catalog

              JonBJ 1 Reply Last reply
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              • Christian EhrlicherC Christian Ehrlicher

                @JonB said in Mysql table locking error:

                LOCK TABLES

                Why do you need it at all?

                JonBJ Offline
                JonBJ Offline
                JonB
                wrote on last edited by
                #10

                @Christian-Ehrlicher
                It's not me, it's the OP!

                @Kutyus wrote:

                The "lock table tablename" is fine, but executing the "unlock tables" gives a false result and the database is stayed in locked state.

                I believe the OP is using LOCK/UNLOCK TABLES. Whether that is a good idea is another matter :) Perhaps they will explain.

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                • SGaistS SGaist

                  Hi,

                  Can you show the code your using ?

                  KutyusK Offline
                  KutyusK Offline
                  Kutyus
                  wrote on last edited by
                  #11

                  @SGaist

                  I derived QSqlQuery and there is an error when I call prepare (), but the factory QSqlQuery also produces an error when prepare () is called but clear () is not.

                  QSqlQuery query = QSqlQuery(db);
                  
                  query.prepare(QString("lock table categories write"));
                  query.exec();
                  
                  query.prepare(QString("update categories set name = '%1' where id = %2").arg(name.text()).arg(id));
                  query.exec();
                  
                  query.clear();
                  query.prepare(QString("unlock tables"));
                  query.exec();
                  
                  JonBJ 1 Reply Last reply
                  0
                  • SGaistS Offline
                    SGaistS Offline
                    SGaist
                    Lifetime Qt Champion
                    wrote on last edited by
                    #12

                    You should check the outcome of each of your queries and print the error if any occurs. That should give you more insight about what is going on.

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

                    KutyusK 1 Reply Last reply
                    0
                    • KutyusK Kutyus

                      @SGaist

                      I derived QSqlQuery and there is an error when I call prepare (), but the factory QSqlQuery also produces an error when prepare () is called but clear () is not.

                      QSqlQuery query = QSqlQuery(db);
                      
                      query.prepare(QString("lock table categories write"));
                      query.exec();
                      
                      query.prepare(QString("update categories set name = '%1' where id = %2").arg(name.text()).arg(id));
                      query.exec();
                      
                      query.clear();
                      query.prepare(QString("unlock tables"));
                      query.exec();
                      
                      JonBJ Offline
                      JonBJ Offline
                      JonB
                      wrote on last edited by
                      #13

                      @Kutyus said in Mysql table locking error:

                      query.prepare(QString("lock table categories write"));

                      You're supposed to take the time to read the documentation (https://dev.mysql.com/doc/refman/8.0/en/lock-tables.html) of your database backend before asking for Qt help here. There is no lock table statement.

                      1 Reply Last reply
                      1
                      • SGaistS SGaist

                        You should check the outcome of each of your queries and print the error if any occurs. That should give you more insight about what is going on.

                        KutyusK Offline
                        KutyusK Offline
                        Kutyus
                        wrote on last edited by
                        #14

                        @SGaist
                        I found a solution, the lock table and the unlock tables statements cannot be prepared, I received the following message:
                        "This command is not supported in the prepared statement protocol yet QMYSQL3: Unable to prepare statement"

                        1 Reply Last reply
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