Important: Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

Selecting data from mysql using qt?



  • 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)
    @



  • Add this to your code after connecting:

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

    And tell us what the error is.



  • [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'?



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

    @db.setPassword("password");@

    ?



  • 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



  • [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 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;
    

    }

    @



  • 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 :)



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



  • 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)

    @



  • any clues?



  • Change the 19th line to

    @QSqlQuery query(db);@



  • same error again



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



  • how can i check that mysql logs and from where?



  • [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@



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



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



  • 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.



  • 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



  • 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.



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



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



  • [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.



  • 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.



  • the file my.cnf is in etc/mysql folder



  • doforumda: use gedit

    sudo gedit /etc/mysql/my.cnf

    at least most of the ubuntu machines have the config file there.



  • this is the socket line in my.cnf

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



  • ok then the wrong socket guess was wrong... but let's make it sure:

    sudo ls -l /var/run/mysqld/*



  • after running this sudo ls -l /var/run/mysqld/* there is nothing inside run directory



  • uhmmmmmmm that's more than strange, the socket file should be there somewhere, let's find it:

    find /var -name mysqld.sock

    if no result:

    find /opt -name mysqld.sock



  • both of them didnt return any resutl

    @
    root@zafar-laptop:/# find /var -name mysqld.sock
    root@zafar-laptop:/# find /opt -name mysqld.sock
    root@zafar-laptop:/#
    @



  • I have bitnami lampp stack installed and when I start it then the socket file is created in /opt/lamppstack/mysql/tmp/mysql.sock. I think doforumda shoudl have similar directory and we need to check the permissions for that directory.



  • Usually that means, that the mysql daemon is not running... but the the command line should not work as well... ;(

    It doesn't hurt to try to start the daemon:

    sudo /etc/init.d/mysql start

    ... and do the search for the socket file as above.



  • gosh, do the find with sudo:

    sudo find /opt -name mysqld.sock
    sudo find /var -name mysqld.sock

    damn, I always forget that with ubuntu



  • lyuts: yes, if he have the socket file at the same place, we need to symlink it to the /var/... location and happy end :) I hope so.



  • tyut: yes i have one file with the name of mysql.sock in /opt/lampp/var/mysql/mysql.sock



  • the permissions on mysql.sock it read write exe for all types of users



  • Great, don't give up, we are close :D

    ls -l /opt/lampp/var/mysql/*

    maybe you have another mysql config file somewhere:

    ls -l /opt/lampp/etc/my.cnf
    or
    ls -l /opt/lampp/etc/mysql/my.cnf
    ?



  • gosh... all with sudo please


Log in to reply