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Creating MySQL plugin for QtCreator, mingw73_64 without full Qt recompile.

  • Hello.

    I've been reading many posts regarding this, but I have some troubles understanding the whole.

    In Qt doc says to make a MySQL "custom install" but there is no "Libs & Include Files" option in their wizard (neither download option in the website). Maybe it's outdated.
    Actually, there is the option for install Connectors.
    Is the "Connectors" the correct MySQL install option?

    There are 3 connectors: C++ 64 bits, C 32 and C64 bits.
    I choose C++... as Qt is for C++, but saw in another post chossing C 32bits connector and nobody says it was wrong.
    What are the correct connector for Qt 64 bits?

    Seems that everything in MySQL is for MSVC compiler. Am I correct?
    Do I need to convert it to mingw-like libraries (.a, if not wrong)? Are the "reimp" and "dlltool" mingw tools, as stated in this post, the way?
    If it's true, why there is nothing about it in Qt Doc?

    In Qt Docs, also, there is some texts with the path where the libs and headers should be installed by default by MySQL wizard. This path is something like MySQL/server..../
    For this reason, I tried to install server, but the libs and headers in there seems not the correct ones.
    Actually, I tried installing server, C++ 8.0 connector and C 6.1 64 bits connector. But the command

    configure -sql-mysql MYSQL_PREFIX=C:\mysql

    reports allways that cannot find mysql header/libs:
    ERROR: Feature 'sql-mysql' was enabled, but the pre-condition 'libs.mysql' failed.

    I would like to compile just the driver.
    When running this command:

    qmake -- MYSQL_INCDIR="c:\mysql\include" MYSQL_LIBDIR="c:\mysql\lib"

    I get this error msg:
    Project ERROR: You cannot configure sqldrivers separately within a top-level build.
    What are the steps for compiling just the driver? I cannot find how to do it.

    Thank you.

  • Lifetime Qt Champion

  • Thanks @Christian-Ehrlicher for your interest.

    Yes I did. Not all the posts because its huge. In fact, there is a link to there in my original post. (where I talk about "reimp" and "dlltool")

    But, you know...Just readed this post once again. It was opened in my browser while my research. I didn't give credit the last answer.
    But... why not try? it's harmless.


    Now I'm able to connect to FreeRadius MySQLi data base!
    4 days.. 4 days reading, testing, frustrating...
    And just copying a file did the trick?
    Why it's not documented as it's so easy?

  • Lifetime Qt Champion


    @Silderan said in Creating MySQL plugin for QtCreator, mingw73_64 without full Qt recompile.:

    Why it's not documented as it's so easy?

    Because, while it's working, it's not the correct solution. The dependencies your application uses should either be findable in the PATH environment variable or copied in the same folder as your application.

    This a Windows specific behaviour.

  • Hello @SGaist

    (I'm really sorry if you didn't mean this. Sometimes it's hard to me to understand english)
    I don't talk about where to put the .dll files.
    The point is that two of the .dll needed are already compiled (both, release and debug, are in .../plugins/sqldrivers)
    Only needed the libmysql.dll, and this is shiped along with MySQL install.
    No need to bulid anything, just copy this .dll in C:\Qt\5.12.0\mingw73_64\bin

    Maybe this is not the correct way as this .dll could not be the correct one and could fail in some scenarios.

    Then... will be good if someone can help to compile it correctly. :P

  • Lifetime Qt Champion

    If it's working it means that the .dll is compatible so you can just use it. What I meant is that copying .dlls around is the wrong thing to do.

    For one reason: if you change your Qt version and the plugin of that version is built with another incompatible version of MySQL, you are going to have a hard time finding why it doesn't load just because you will likely have forgotten that you copied that .dll there.

  • Agree. But...
    What about my original question(s)? XD
    Solving this, I will be closer to compile and won't be worried about .dll version mismatch. ;)

  • Lifetime Qt Champion

    Did you run qmake inside the MySQL plugin folder ?

  • 0_1549725440560_faff53a0-5191-47d3-a29f-523beaa31968-image.png


    But, If I'm not wrong, this is because of...:

    Also, found this:

    Sadly, this is far beyond my knowledge.

  • Lifetime Qt Champion

    Since configure failed, did you check the reason of the failure ?

  • Found this in config.log:

    loaded result for library config.qtbase_sqldrivers.libraries.mysql
    Trying source 0 (type mysqlConfig) of library mysql ...
    mysql_config not found.
      => source produced no result.
    Trying source 1 (type mysqlConfig) of library mysql ...
    mysql_config not found.
      => source produced no result.
    Trying source 2 (type mysqlConfig) of library mysql ...
    mysql_config not found.
      => source produced no result.
    Trying source 3 (type mysqlConfig) of library mysql ...
    mysql_config not found.
      => source produced no result.
    Trying source 4 (type inline) of library mysql ...
      => source failed condition '!config.win32'.
    Trying source 5 (type inline) of library mysql ...
    + cd /d C:\Qt\5.12.0\Src\config.tests\mysql && C:\Qt\5.12.0\Src\qtbase\bin\qmake.exe "CONFIG -= qt debug_and_release app_bundle lib_bundle" "CONFIG += shared warn_off console single_arch" "QMAKE_USE += mysql" "QMAKE_LIBS_MYSQL = -LC:\\mysql/lib -llibmysql" "QMAKE_INCDIR_MYSQL = C:\\mysql/include" C:/Qt/5.12.0/Src/config.tests/mysql
    + cd /d C:\Qt\5.12.0\Src\config.tests\mysql && set MAKEFLAGS=& mingw32-make
    > g++ -c -fno-keep-inline-dllexport -g -w -fexceptions -mthreads -DUNICODE -D_UNICODE -DWIN32 -DMINGW_HAS_SECURE_API=1 -I. -IC:\mysql\include -IC:\Qt\5.12.0\Src\qtbase\mkspecs\win32-g++  -o main.o main.cpp
    > main.cpp:5:10: fatal error: mysql.h: No such file or directory
    >  #include <mysql.h>
    >           ^~~~~~~~~

    But I wasn't able to figure out nor why cannot find the header (path is correct) neither how to change it (changing MYSQL_PREFIX=C:\mysql makes no diference. As if this is not the correct syntax)
    Furthermore, by executing this three commands out of configure script shows no error:

  • Lifetime Qt Champion

    MYSQL_PREFIX is for Unix like OSes.

    You should also use forward slashes for your paths.

  • Well then... don't blame me. It's official doc info:


    Furthermore I tried forward slashes, backward slashes, double backward...
    No change at all :P (Remember what I said... using the same commands out of script, mysql libraries test compiles! Even mixing forward and backward slashes)

    Anyway, if MYSQL_PREFIX is not for Window. Why it is in official doc and witch one must we use?

  • Lifetime Qt Champion

    Then please re-read said documentation
    You have a clear separation with:
    How to Build the QMYSQL Plugin on Unix and macOS
    and below you have:
    How to Build the QMYSQL Plugin on Windows

    So the technique for each is well separated.

    And you are mixing the information for the configure script or for building using qmake.

  • Once you said:

    @SGaist said in Creating MySQL plugin for QtCreator, mingw73_64 without full Qt recompile.:

    Since configure failed, did you check the reason of the failure ?

    I figure out that I must run a success configure at first. Sorry for the confusion. My lasts posts were about configure tool, not building the plugins.
    I'm not able to figure out the reason of the failure. Seems like test code is not able to get the header files, as if the headers don't exists or the include path is wrong. But my "out of the box" tests works.

    Anyway, I even tried MYSQL_INCDIR and MYSQL_LIBDIR instead of *_PREFIX in configure step. Same result:

    Sorry again for not been clear enough.

  • Lifetime Qt Champion

    One thing you can try is to use the "-I" and "-L" options of the configure script passing there the paths to your MySQL include and library folder.

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