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Selecting data from mysql using qt?

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  • L Offline
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    lyuts
    wrote on 12 Oct 2010, 10:03 last edited by
    #71

    Add this to your code after connecting:

    @qDebug() << db.lastError().text();@

    And tell us what the error is.

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

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    • L Offline
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      lyuts
      wrote on 12 Oct 2010, 10:04 last edited by
      #72

      [quote author="doforumda" date="1286877766"]wait i think the query is not sucessful because it displays this message 0 rows affected
      @
      mysql> grant all on testTwo.* to 'root'at'localhost' identified by 'password';
      Query OK, 0 rows affected (0.01 sec)
      @[/quote]

      Did you run that command with 'password' instead of '123456'?

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

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      • D Offline
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        Dii
        wrote on 12 Oct 2010, 10:05 last edited by
        #73

        0 rows is just fine with the grant command... have you set the password on

        @db.setPassword("password");@

        ?

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        • D Offline
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          doforumda
          wrote on 12 Oct 2010, 10:09 last edited by
          #74

          this is the output after adding lastError.text()
          @
          Starting /home/zafar/c++/dbExample-build-desktop/dbExample...
          " "
          false
          QSqlQuery::exec: database not open
          /home/zafar/c++/dbExample-build-desktop/dbExample exited with code 0
          @

          lyut: yes i use command with 'password' not '123456'

          Dii sorry i didnt understand this db.setPassword("password");
          where should i set this

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          • L Offline
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            lyuts
            wrote on 12 Oct 2010, 10:13 last edited by
            #75

            [quote author="doforumda" date="1286878193"]
            lyut: yes i use command with 'password' not '123456'

            Dii sorry i didnt understand this db.setPassword("password");
            where should i set this[/quote]

            1. I assume you should have specified the actual password when running that query.
            2. @db.setPassword("password");@ should be added to your source code just where you set db options.

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

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            • D Offline
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              doforumda
              wrote on 12 Oct 2010, 10:15 last edited by
              #76

              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 Offline
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                Dii
                wrote on 12 Oct 2010, 10:18 last edited by
                #77

                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 Offline
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                  lyuts
                  wrote on 12 Oct 2010, 10:21 last edited by
                  #78

                  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 Offline
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                    doforumda
                    wrote on 12 Oct 2010, 10:24 last edited by
                    #79

                    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 Offline
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                      doforumda
                      wrote on 12 Oct 2010, 10:38 last edited by
                      #80

                      any clues?

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                      • L Offline
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                        lyuts
                        wrote on 12 Oct 2010, 10:41 last edited by
                        #81

                        Change the 19th line to

                        @QSqlQuery query(db);@

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

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                          doforumda
                          wrote on 12 Oct 2010, 10:43 last edited by
                          #82

                          same error again

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                          • L Offline
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                            lyuts
                            wrote on 12 Oct 2010, 10:46 last edited by
                            #83

                            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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                              doforumda
                              wrote on 12 Oct 2010, 10:49 last edited by
                              #84

                              how can i check that mysql logs and from where?

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                              • L Offline
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                                lyuts
                                wrote on 12 Oct 2010, 10:54 last edited by
                                #85

                                [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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                                  doforumda
                                  wrote on 12 Oct 2010, 10:56 last edited by
                                  #86

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

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                                    doforumda
                                    wrote on 12 Oct 2010, 11:01 last edited by
                                    #87

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

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                                    • L Offline
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                                      lyuts
                                      wrote on 12 Oct 2010, 11:01 last edited by
                                      #88

                                      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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                                        doforumda
                                        wrote on 12 Oct 2010, 11:03 last edited by
                                        #89

                                        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 Offline
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                                          Dii
                                          wrote on 12 Oct 2010, 11:04 last edited by
                                          #90

                                          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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                                          80/150

                                          12 Oct 2010, 10:38

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