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    Call for Presentations - Qt World Summit

    Selecting data from mysql using qt?

    General and Desktop
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    • D
      doforumda last edited by

      i ran query again with actual password
      i have already setup password in my qt code here it is
      @
      #include <QApplication>
      #include <QtSql>

      int main(int argc, char *argv[])
      {
      QCoreApplication a(argc, argv);

      QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
      db.setDatabaseName("testTwo");
      db.setUserName("root");
      db.setPassword("123456");
      db.setHostName("localhost");
      
      qDebug() << db.lastError().text();
      
      bool ok = db.open();
      qDebug() << ok;
      
      QSqlQuery query;
      query.exec&#40;"SELECT firstname,lastname FROM testTable"&#41;;
      while(query.next()) {
          QString firstName = query.value(0).toString();
          QString secondName = query.value(1).toString();
          qDebug() << "First Name: " << firstName << "Last Name:" << secondName;
          qDebug() << db.lastError();
      }
      return 0;
      

      }

      @

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      • D
        Dii last edited by

        db.lasterror().text() should come after line 16 (db.open()).
        The password in the Qt code must be the same what you have specified in the GRANT command above.

        I suspect probably, you haven't made the database and the table in mysql yet, if you go back to mysql command line, what do you get by these commands:

        @SHOW databases;

        USE testTwo;

        SHOW tables;@

        I go to dinner, be back in a few minutes :)

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        • L
          lyuts last edited by

          You put my debug before opening the connection. Put it after.

          I'm a rebel in the S.D.G.

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          • D
            doforumda last edited by

            i changed db.lastError().text(); and place it after db.open()
            this is the output
            @
            Starting /home/zafar/c++/dbExample-build-desktop/dbExample...
            "Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2) QMYSQL: Unable to connect"
            false
            QSqlQuery::exec: database not open
            /home/zafar/c++/dbExample-build-desktop/dbExample exited with code 0
            @

            the commands in mysql displayed are here
            repectively to your commands

            @
            mysql> show databases;
            +--------------------+
            | Database |
            +--------------------+
            | information_schema |
            | cdcol |
            | mysql |
            | phpmyadmin |
            | test |
            | testTwo |
            +--------------------+
            6 rows in set (0.01 sec)

            mysql> use testTwo
            Database changed
            mysql> show tables
            -> ;
            +-------------------+
            | Tables_in_testTwo |
            +-------------------+
            | testTable |
            +-------------------+
            1 row in set (0.01 sec)

            @

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            • D
              doforumda last edited by

              any clues?

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              • L
                lyuts last edited by

                Change the 19th line to

                @QSqlQuery query(db);@

                I'm a rebel in the S.D.G.

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                • D
                  doforumda last edited by

                  same error again

                  1 Reply Last reply Reply Quote 0
                  • L
                    lyuts last edited by

                    Take a look into mysql logs to see what happens when you are trying to connect from your application.

                    I'm a rebel in the S.D.G.

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                    • D
                      doforumda last edited by

                      how can i check that mysql logs and from where?

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                      • L
                        lyuts last edited by

                        [quote author="doforumda" date="1286880547"]how can i check that mysql logs and from where? [/quote]

                        Try to find them:
                        @find /opt/lampp -name log -type d@

                        When you find the log directory, find a log for mysql and use tail utility:

                        @tail -f /path/to/mysql.log@

                        I'm a rebel in the S.D.G.

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                        • D
                          doforumda last edited by

                          this command didnt return something
                          @
                          root@zafar-laptop:/# find /opt/lampp -name log -type d
                          root@zafar-laptop:/#
                          @

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                          • D
                            doforumda last edited by

                            i have a folder inside lampp with the name logs. is it the one which your are talking about

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                            • L
                              lyuts last edited by

                              Solution 1:
                              @find /opt/lampp -name '*.log'@
                              This might need sudo'ing.

                              Solution 2:
                              If 1st fails then you need to find the config files for mysql (it should be located in /opt/lampp directory) and try to find out what is the location of mysql's log files.

                              I'm a rebel in the S.D.G.

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                              • D
                                doforumda last edited by

                                there are 6 files in there but no mysql.log

                                these are the files
                                access_log, cgisock.1693, error_log, httpd.pid, php_error_log, ssl_request_log

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                                • D
                                  Dii last edited by

                                  Don't bother with the log files, I guess Qt looks at the wrong place for the socket file...

                                  Let's check this line in your mysql config file (my.cnf):

                                  socket = /var/run/mysqld/mysqld.sock

                                  You should find my.cnf in /etc/ or /etc/mysql/ ... I don't know ubuntu that much.

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                                  • D
                                    doforumda last edited by

                                    1st solution returns this
                                    @
                                    root@zafar-laptop:/# find /opt/lampp -name *.log
                                    /opt/lampp/htdocs/xampp/contrib/sqlnet.log
                                    @

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                                    • D
                                      doforumda last edited by

                                      with which editor i can view that .conf file. with gedit or something.

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                                      • L
                                        lyuts last edited by

                                        [quote author="¤ Dii ¤" date="1286881470"]
                                        You should find my.cnf in /etc/ or /etc/mysql/ ... I don't know ubuntu that much.[/quote]

                                        I don't think that this config will be in /etc. He uses lampp - a preconfigured bundle. That config might be in /opt/lampp.

                                        I'm a rebel in the S.D.G.

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                                        • D
                                          Dii last edited by

                                          BTW a quick sum:

                                          • mysql is installed
                                          • database and tables are created
                                          • access is granted
                                          • qt code looks fine

                                          I see two possibilities here: libmysqlclient is missing, or the socket file is at different place.

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                                          • D
                                            doforumda last edited by

                                            the file my.cnf is in etc/mysql folder

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