Cannot connect to MySQL server

t0msk

Hello, I cannot connect to MySQL server using this code:

loader.cpp:

#include "QMessageBox"
#include <QSqlDatabase>
#include <QSqlDriver>
#include <QSqlError>
#include <QSqlQuery>
#include "QDebug"

QSqlDatabase db2 = QSqlDatabase::addDatabase("QMYSQL");
    db2.setHostName("127.0.0.1");
    db2.setDatabaseName("pve");
    db2.setUserName("root");
    db2.setPassword("test123");
    if(!db2.open())
        QMessageBox::critical(this,"Error","Unable to connect to the database");

PVE.pro:

#-------------------------------------------------
#
# Project created by QtCreator 2017-01-31T22:29:06
#
#-------------------------------------------------

QT       += core gui sql

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = PVE
TEMPLATE = app
CONFIG += thread


SOURCES += main.cpp\
        loader.cpp \
    mainwindow.cpp \
    global.cpp

HEADERS  += loader.h \
    mainwindow.h \
    global.h

FORMS    += loader.ui \
    mainwindow.ui

If I set same login details into MySQL workbench I will log with no problems.

Can you help me please? :/

koahnig

@t0msk

you can check with QSqlDatabase::isDriverAvailable("QMYSQL") if the driver is available.

t0msk

I added:

bool test = QSqlDatabase::isDriverAvailable("QMYSQL");

And i got true, so driver is probably ok.

koahnig

@t0msk

I have compared with my implementation the only difference was the driver test.

Another thing is that you are not linking with an SQL library. In my case I have

LIBS += -llibmysql

However, that should give you already a link error.

t0msk

I got an error:

error: cannot find -llibmysql

Why there is " - " in:

LIBS += -llibmysql

?

mateczek

https://youtu.be/0qjcVg-8Vgw?t=210
polish language but you must have :

download mysql c connector
copy libmysql.dll to bin folder (start app from qtcreator)
3 . copy libmysql.dll to build folder (start application from double clicked on exe file)
copy plugin folder to folder with your program (start application from double clicked on exe file)

In my project I never don't need this

LIBS += -llibmysql

to correctly connect to db!!!

koahnig

@t0msk

Sorry, did not think that this may work in your case. However, are you linking with a MySql library?
I would guess so, because otherwise you should not be able to link and run the application.

What is your operation system?

t0msk

@mateczek said in Cannot connect to MySQL server:

https://youtu.be/0qjcVg-8Vgw?t=210
polish language but you must have :

download mysql c connector

copy libmysql.dll to bin folder (start app from qtcreator)
3 . copy libmysql.dll to build folder (start application from double clicked on exe file)

copy plugin folder to folder with your program (start application from double clicked on exe file)

In my project I never don't need this
LIBS += -llibmysql
to correctly connect to db!!!

Thank you it works ^^

@koahnig said in Cannot connect to MySQL server:

@t0msk

Sorry, did not think that this may work in your case. However, are you linking with a MySql library?
I would guess so, because otherwise you should not be able to link and run the application.

What is your operation system?

So problem is solved, my OS is Windows 7, but I wonder why SQL connector is not built in Qt, it is quite common thing.

mateczek

on widnows You must download "mysql c connector" :(

on ubuntu You must install

sudo apt-get install libmysqlclient-dev

t0msk

@mateczek said in Cannot connect to MySQL server:

on widnows You must download "mysql c connector" :(

on ubuntu You must install
sudo apt-get install libmysqlclient-dev

Good to know, because I have some Linux machines :)

koahnig

@t0msk said in Cannot connect to MySQL server:

So problem is solved, my OS is Windows 7, but I wonder why SQL connector is not built in Qt, it is quite common thing.

Probably because of license issues it cannot be included in the distribution.

t0msk

@koahnig said in Cannot connect to MySQL server:

@t0msk said in Cannot connect to MySQL server:

So problem is solved, my OS is Windows 7, but I wonder why SQL connector is not built in Qt, it is quite common thing.

Probably because of license issues it cannot be included in the distribution.

Ah ok, thank you :)

t0msk

@mateczek said in Cannot connect to MySQL server:

on widnows You must download "mysql c connector" :(

on ubuntu You must install
sudo apt-get install libmysqlclient-dev

Sorry for opening older topic, but how to fix missing driver on Ubuntu? I run sudo apt-get install libmysqlclient-dev

tomsk@tomsk-U36SD:~/Qt/5.7/gcc_64/plugins/sqldrivers$ sudo apt-get install libmysqlclient-dev
Reading package lists... Done
Building dependency tree       
Reading state information... Done
libmysqlclient-dev is already the newest version (5.7.17-0ubuntu0.16.04.1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
tomsk@tomsk-U36SD:~/Qt/5.7/gcc_64/plugins/sqldrivers$

And this is error from Qt

QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers: QSQLITE QMYSQL QMYSQL3 QPSQL QPSQL7

SGaist

Hi,

Rebuild the Qt MySQL plugin.

If you call ldd on the plugin you'll see that the linked libraries are not the same as the one you installed. That's normal, don't worry, just rebuild the plugin.

t0msk

I never rebuilded plugin, how to do that?

I found:

cd $QTDIR/src/plugins/sqldrivers/mysql
qmake "INCLUDEPATH+=/usr/local/include" "LIBS+=-L/usr/local/lib -lmysqlclient_r" mysql.pro
make

But

tomsk@tomsk-U36SD:~$ cd $QTDIR/src/plugins/sqldrivers/mysql
bash: cd: /src/plugins/sqldrivers/mysql: No such file or directory

Where should be $QTDIR?

SGaist

Did you download the sources from your Qt version ? It can be done through the installer.

jsulm

@t0msk said in Cannot connect to MySQL server:

Where should be $QTDIR

Where your Qt installation containing src subfolder is.