QSqlDatabase: QMYSQL driver not loaded

ThiagoSys

Hello, my english is not the best but i will try.

Im developing an application in python and Qt Designer with PyQt6. I want to use QSqlDatabase and QSqlTableView. My first problem when connecting QSqlDatabase to mysql was the connection failure due to the lack of the plugin for mysql, where te message "QSqlDatabase: available drivers: QSQLITE QMIMER QODBC QPSQL" was returned. Searching the forums for a solution, I found several tutorials on how to compile the plugin, but most of my attempts failed, I believe because I installed Qt version 6.8.1 to carry out the compilation, which from what some people returned was not working well.

Until I found the video linked below https://youtu.be/5NypUQ5AtgU and decided to install version 6.7.3 to try to compile, which gave a positive result carrying out the compilation as shown in the video. After compiling, i copy the mysql archives from "C:\Qt\6.7.3\mingw_64\plugins\sqldrivers" to "C:\Users\thiag\AppData\Local\Programs\Python\Python313\Lib\site-packages\PyQt6\Qt6\plugins\sqldrivers" which is my python installation directory. I saw this last step in some of the posts and in a way it worked, since the return message is now "QSqlDatabase: available drivers: QSQLITE QMIMER QMARIADB QMYSQL QODBC QPSQL" but the connection still does not occur. Remembering that I am using python in visual studio code and PyQt6. I would like to know what else I need to do to make everything work well, or if I did something wrong in the process. Below I leave the code for the connection part and thank you in advance for your help.

self.dbQSql = QSqlDatabase.addDatabase("QMYSQL")  # Driver for MySQL
self.dbQSql.setHostName(dbMysql.host)
self.dbQSql.setUserName(dbMysql.user)
self.dbQSql.setPassword(dbMysql.password)
self.dbQSql.setDatabaseName(dbMysql.database)

JonB

@ThiagoSys
Because you now have QMYSQL as a listed driver you have done that part correctly.

Now set environment variable QT_DEBUG_PLUGINS=1 and then run your code. You will get lots of diagnostic output. Look through it for QMYSQL, particularly at the end of the output, it should tell you why it cannot be loaded (usually missing dependencies).

On a separate matter: although it is not the cause of your current issue, nonetheless as per the docs you ought not store a reference to a SQL database in a self class variable (self.dbQSql = QSqlDatabase.addDatabase("QMYSQL")). You should rather store that in a local variable, and use QSqlDatabase.database() when you want to access it again later on.

ThiagoSys

Should I run the command "export QT_DEBUG_PLUGINS=1" with the terminal in which directory? Forgot to mention but I'm on Windows

SGaist

Hi,

If you are running from the command line, yes.
Otherwise, you can do that in your Python script with os module before doing anything Qt. Or if you are using an IDE, it should provide a mean to change the environment variables.

From experience, you will likely have a message stating that the dependencies of the MySQL plugin cannot be found.

ThiagoSys

I managed to activate the more detailed messages and the result was

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("QPSQL")
qt.core.plugin.factoryloader: checking directory path "C:/Users/thiag/AppData/Local/Programs/Python/Python313/sqldrivers" ...
qt.core.library: "C:/Users/thiag/AppData/Local/Programs/Python/Python313/Lib/site-packages/PyQt6/Qt6/plugins/sqldrivers/qsqlmysql.dll" cannot load: Cannot load library C:\Users\thiag\AppData\Local\Programs\Python\Python313\Lib\site-packages\PyQt6\Qt6\plugins\sqldrivers\qsqlmysql.dll: Não foi possível encontrar o procedimento especificado.
qt.core.plugin.loader: QLibraryPrivate::loadPlugin failed on "C:/Users/thiag/AppData/Local/Programs/Python/Python313/Lib/site-packages/PyQt6/Qt6/plugins/sqldrivers/qsqlmysql.dll" : "Cannot load library C:\Users\thiag\AppData\Local\Programs\Python\Python313\Lib\site-packages\PyQt6\Qt6\plugins\sqldrivers\qsqlmysql.dll: Não foi possível encontrar o procedimento especificado."

SGaist

I did not realize...
You might be mixing and matching Qt versions and compilers which is a no go.
Did you check which version of Qt is PyQt6 using ?
Did you verify that you are using the same compiler to build the plug-in that was used for PyQt6 ?

ThiagoSys

In the video that I used as a base, the mingw compiler was used, I believe that this is not the one used by Qt. How can I check the version that PyQt6 is using and which compiler it is?

ThiagoSys

Hello again.

I managed to compile the plugin correctly using msvc using version 6.7.3 but it returned the error

Cannot mix incompatible Qt library (6.7.3) with this library (6.8.1)

So I tried to do the same process in version 6.8.1, but when running the command

call C:\Qt\6.8.1\msvc2022_64\bin\qt-cmake.bat -G "Ninja" . -DMySQL_INLCUDEDIR="C:\Program Files\MySQL\MySQL Server 8.0\include" -DMySQL_LIBRARY="C:\Program Files\MySQL\MySQL Server 8.0\lib\libmysql.lib" -DCMAKE_INSTALL_PREFIX="C:\Qt\6.8 .1\msvc2022_64"

I get the error

-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - not found

Is this a problem with version? I used the same method that had worked in version 6.7.3. If it's a version issue, will I have to wait for a new version to be released by PyQt6?

Christian Ehrlicher

@ThiagoSys said in QSqlDatabase: QMYSQL driver not loaded:

I get the error

I don't see any error here, just information on what features are found/not found.

ThiagoSys

This post is deleted!

Christian Ehrlicher

See https://forum.qt.io/search?in=posts&term=sbom&matchWords=all&by=&categories=&searchChildren=false&hasTags=&replies=&repliesFilter=atleast&timeFilter=newer&timeRange=&sortBy=relevance&sortDirection=desc&showAs=posts

ThiagoSys

@Christian-Ehrlicher

You said in one of the posts linked above to Update to 6.8.2 / 6.9.0
But when I run my code with plugin version 6.7.3 I got the following error
Cannot mix incompatible Qt library (6.7.3) with this library (6.8.1)

If I install version 6.8.2 wouldn't this incompatibility happen in the same way?

Christian Ehrlicher

I also wrote that you can apply the patch...

ThiagoSys

@Christian-Ehrlicher Can you provide me with an explanation on how to apply the patch?

ThiagoSys

Can anyone tell me how to compile SBOM?

SGaist

From the looks of it, you can also disable the sbom. See this comment on the bug report.

As for patching, do you know how to apply a diff ?
If not, one possible solution is to just copy the two files from 6.8.2 into your current sources but I would encourage you to learn how to apply a patch.

ThiagoSys

@SGaist
I tried to learn how to apply a patch but it's complicated, I'm Brazilian and I can't find much about it in Portuguese.
About disabling sbom I tried adding the commands -DQT_GENERATE_SBOM=OFF and -no-sbom but it didn't change. I'm thinking about giving up and doing it the traditional way

jsulm

@ThiagoSys What about this suggestion from @SGaist : "one possible solution is to just copy the two files from 6.8.2 into your current sources"?

And applying patches isn't isn't complicated.

ThiagoSys

@jsulm
I don't know exactly which files I should copy and to which source

SGaist

If you go to the patch linked in the bug report, you'll see the exact path of the two files that have been modified in qtbase.