Missing MySql driver when using PySide2 QtSql QSqlDatabase

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I'm porting some code from PySide to PySide2 and I've noticed that I'm missing a couple of sql drivers.

$ python3
Python 3.6.8 (default, Apr  2 2020, 13:34:55) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-39)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import PySide.QtSql; import PySide2.QtSql
>>> PySide.QtSql.QSqlDatabase.drivers()
['QSQLITE', 'QSQLITE3', 'QMYSQL3', 'QMYSQL', 'QODBC3', 'QODBC', 'QPSQL7', 'QPSQL']
>>> PySide2.QtSql.QSqlDatabase.drivers()
['QSQLITE', 'QODBC', 'QODBC3', 'QPSQL', 'QPSQL7']

As you can see I'm missing QMYSQL on PySide2 (among others). I need that one for my application to work.

I've tried installing a couple of packages like mysql mysql-connector-python through pip but that didn't change anything. Then I tried changing QTDIR because I noticed it was pointing to /usr/lib64/qt-3.3 instead of /usr/lib64/qt5. That didn't do anything either.

I also checked /usr/lib64/qt4/plugins/sqldrivers and /usr/lib64/qt5/plugins/sqldrivers for libqsqlmysql.so and it's present in both folders.

I'm on CentOS 7 by the way. I'm trying to get the software on CentOS 7 and 8, though.

Pretty much all of the posts I've seen about it the drivers aren't missing but they can't be loaded.

Any idea what could be the problem?

centos7 pyside2 python-3.x mysql python
1 Answers

Most likely, the plugin directory is not in "/usr/lib64/qt5/plugins" so it doesn't load the mysql plugin. The solution is to copy the plugin so the first thing is to know the PySide2 directory plugin by executing the following command:

$ python3 -c "from PySide2 import QtCore; print(QtCore.QLibraryInfo.location(QtCore.QLibraryInfo.PluginsPath))"

Output:

/usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins

So you should copy the .so using the following command:

$ cp /usr/lib64/qt5/plugins/sqldrivers/libqsqlmysql.so /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers

Even so the .so points to the Qt of the OS instead of the Qt of PySide2:

$ ldd  /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers/libqsqlmysql.so

Output

linux-vdso.so.1 =>  (0x00007fffb974f000)
libQt5Sql.so.5 => /lib64/libQt5Sql.so.5 (0x00007faa76f00000)
libQt5Core.so.5 => /lib64/libQt5Core.so.5 (0x00007faa76895000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007faa76679000)
libmysqlclient.so.18 => /usr/lib64/mysql/libmysqlclient.so.18 (0x00007faa76179000)
# ...

for this you must change the rpath using patchelf:

$ yum install epel-release
$ yum install patchelf
$ patchelf --set-rpath \$ORIGIN/../../lib  /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers/libqsqlmysql.so

again:

$ ldd  /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers/libqsqlmysql.so

Output

linux-vdso.so.1 =>  (0x00007ffd013ad000)
libQt5Sql.so.5 => /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers/../../lib/libQt5Sql.so.5 (0x00007f6e1fb4c000)
libQt5Core.so.5 => /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers/../../lib/libQt5Core.so.5 (0x00007f6e1f359000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f6e1f13d000)
libmysqlclient.so.18 => /usr/lib64/mysql/libmysqlclient.so.18 (0x00007f6e1ec3d000)
# ...

Finally:

$ python3 -c "from PySide2 import QtSql; print(QtSql.QSqlDatabase.drivers())"

Output:

['QSQLITE', 'QMYSQL', 'QMYSQL3', 'QODBC', 'QODBC3', 'QPSQL', 'QPSQL7']

It seems that there is no binary compatibility between the plugins so it must be compiled using the source code:

$ python3 -m pip install aqtinstall
$ python3 -m aqt install 5.15.0 linux desktop --outputdir qt
$ sudo yum -y install git
$ sudo yum -y install libxcb libxcb-devel xcb-util xcb-util-devel xcb-util-*-devel libX11-devel libXrender-devel libxkbcommon-devel libxkbcommon-x11-devel libXi-devel libdrm-devel libXcursor-devel libXcomposite-devel
$ sudo yum -y install centos-release-scl
$ sudo yum -y install devtoolset-7-gcc*
$ sudo yum -y groupinstall 'Development Tools'
$ sudo yum -y install mysql-devel
$ scl enable devtoolset-7 bash
$ git clone -b 5.15.0 git://code.qt.io/qt/qtbase.git
$ cd qtbase/src/plugins/sqldrivers/mysql
$ sed -i 's/QMAKE_USE += mysql/# QMAKE_USE += mysql/g' mysql.pro
$ echo "INCLUDEPATH += /usr/include/mysql" >> mysql.pro
$ echo "QMAKE_LIBDIR += /usr/lib64/mysql" >> mysql.pro
$ echo "LIBS += -lmysqlclient" >> mysql.pro
$ ../../../../../qt/5.15.0/gcc_64/bin/qmake
$ make
$ sudo cp ../plugins/sqldrivers/libqsqlmysql.so /usr/local/lib64/python3.6/site-packages/PySide2/Qt/plugins/sqldrivers

Finally:

$ python3 -c "from PySide2 import QtSql; print(QtSql.QSqlDatabase.drivers())"

Output:

['QSQLITE', 'QMARIADB', 'QMYSQL', 'QMYSQL3', 'QODBC', 'QODBC3', 'QPSQL', 'QPSQL7']
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