无法在 PySide2 上加载 QMYSQL 驱动程序

Question

How can i install and load the Qmysql driver using Pyside2 (pip) with python3.8? I've already tried to download git:qtbase and compiled the driver from there but I had any luck.

Answer 1

_{This answer covers not only the installation for Linux but for the other OS, besides that it also applies for pyqt5}

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The binaries used by Qt are the same ones used by PyQt5/PySide2 since they use the same base code so you will have to compile the plugins.

In this case, to compile the mysql plugin you must follow the official manual , which in summary is:

1. Install the dependencies, in this case the mysql-connector-c
2. Install Qt of the same version with which pyqt5/pyside2 was compiled and development tools such as MSVC on windows, build-essentials on Ubuntu, XCode on MacOS, etc.
3. Download the source code, in this case the qtbase repository .
4. Compile the plugin.

To find out the version of Qt with the version that the library was compiled with, the following can be used:

• PyQt5

python -c "from PyQt5.QtCore import QT_VERSION_STR; print('Qt version', QT_VERSION_STR)"

• PySide2

python -c "from PySide2.QtCore import qVersion; print('Qt version', qVersion())"

The above generates libqsqlmysql.so, qsqlmysql.dll or libqsqlmysql.dylib depending on the OS. That file must be pasted in the path:

• PyQt5:

python -c "import os; from PyQt5.QtCore import QLibraryInfo; print('QT_SQL_DRIVER_PATH', os.path.join(QLibraryInfo.location(QLibraryInfo.PrefixPath), 'plugins', 'sqldrivers'))"

• PySide2:

python -c "import os; from PySide2.QtCore import QLibraryInfo; print('QT_SQL_DRIVER_PATH', os.path.join(QLibraryInfo.location(QLibraryInfo.PrefixPath), 'plugins', 'sqldrivers'))"

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To cover all the cases I have created a Github Actions that generates the binaries:

mysql_plugin.yml

name: generate_mysql_plugin

on: [push]

jobs:
  ci:
    name: ${{ matrix.os.name }} Qt-${{ matrix.qt.qt_version }}
    runs-on: ${{ matrix.os.runs-on }}
    strategy:
      fail-fast: false
      matrix:
        os:
          - name: Windows
            extension: "dll"
            runs-on: windows-2019
          - name: Linux
            extension: "so"
            runs-on: ubuntu-20.04
          - name: MacOS
            extension: "dylib"
            runs-on: macos-10.15
        qt:
          - name: 5.15
            qt_version: 5.15.0
    steps:
      - name: Checkout
        uses: actions/checkout@v1
      - name: Install Qt
        uses: jurplel/install-qt-action@v2
        with:
          version: ${{ matrix.qt.qt_version }}
          dir: ${{ github.workspace }}/qt/
      - name: clone qtbase
        run: git clone -b ${{ matrix.qt.qt_version }} https://code.qt.io/qt/qtbase.git
      - name: Compile mysql plugin on Windows
        if: matrix.os.name == 'Windows'
        shell: cmd
        run: |
          choco install wget
          wget https://downloads.mysql.com/archives/get/p/19/file/mysql-connector-c-6.1.11-winx64.zip
          unzip mysql-connector-c-6.1.11-winx64.zip
          copy /y "mysql-connector-c-6.1.11-winx64\lib\libmysql.dll" .
          call "C:/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/VC/Auxiliary/Build/vcvars64.bat"
          cd qtbase/src/plugins/sqldrivers
          qmake -- MYSQL_INCDIR="${{ github.workspace }}\mysql-connector-c-6.1.11-winx64\include" MYSQL_LIBDIR="${{ github.workspace }}\mysql-connector-c-6.1.11-winx64\lib"
          nmake sub-mysql
          nmake install
      - name: Compile mysql plugin on Linux
        if: matrix.os.name == 'Linux'
        run: |
          wget https://downloads.mysql.com/archives/get/p/19/file/mysql-connector-c-6.1.11-linux-glibc2.12-x86_64.tar.gz
          tar zxvf mysql-connector-c-6.1.11-linux-glibc2.12-x86_64.tar.gz
          sudo cp mysql-connector-c-6.1.11-linux-glibc2.12-x86_64/lib/*.so /usr/lib/x86_64-linux-gnu
          sudo apt-get install freetds-dev
          cd qtbase/src/plugins/sqldrivers
          qmake
          cd mysql
          qmake
          make
          make install
      - name: Compile mysql plugin on MacOS
        if: matrix.os.name == 'MacOs'
        run: |
          brew install wget
          wget https://cdn.mysql.com/archives/mysql-connector-c/mysql-connector-c-6.1.11-macos10.12-x86_64.tar.gz
          tar zxvf mysql-connector-c-6.1.11-macos10.12-x86_64.tar.gz
          sudo cp mysql-connector-c-6.1.11-macos10.12-x86_64/lib/libmysqlclient.dylib mysql-connector-c-6.1.11-macos10.12-x86_64/lib/libmysqlclient_r.dylib
          sudo cp mysql-connector-c-6.1.11-macos10.12-x86_64/lib/libmysqlclient.18.dylib mysql-connector-c-6.1.11-macos10.12-x86_64/lib/libmysqlclient_r.18.dylib

          sudo cp mysql-connector-c-6.1.11-macos10.12-x86_64/lib/*.dylib /usr/local/lib
          cd qtbase/src/plugins/sqldrivers
          qmake -- MYSQL_PREFIX="${{ github.workspace }}/mysql-connector-c-6.1.11-macos10.12-x86_64"
          make sub-mysql
          cd mysql
          make install
      - name: upload
        uses: actions/upload-artifact@v2
        with:
          path: qtbase/src/plugins/sqldrivers/plugins/sqldrivers/*qsqlmysql.${{ matrix.os.extension }}
          name: mysqlplugin-${{ matrix.os.name }}-Qt${{ matrix.qt.name }}

The previous code generates the plugin that you can find here .

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In the specific case of Ubuntu it can be reduced to:

• Copy the libqsqlmysql.so file to QT_SQL_DRIVER_PATH.
• Execute sudo apt install libmysqlclient-dev

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In the specific case of Windows it can be reduced to:

• Copy the qsqlmysql.dll file to QT_SQL_DRIVER_PATH.
• Download the mysql-connector-c for windows and copy the libmysql.dll next to your script.

Answer 2

PS almost half of this info is officially published at https://doc.qt.io/qt-6/deployment-plugins.html

I use PySide6 on Windows 10 and %QT_SQL_DRIVER_PATH% does not work for me. What works for PySide6 is the %QT_PLUGIN_PATH% environment variable.

Let's assume that you have built (or downloaded) a SQL driver for Qt platform into C:\projects\my-project-1\qt-plugins\sqldrivers , so that there is qsqlmysql.dll there.

CASE #1: you execute QSqlDatabase.addDatabase("QMYSQL") , but you get the following error:

QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers: QSQLITE QODBC QPSQL

It means that qsqlmysql.dll (a plugin for Qt platform) was not found.

The fix is to define the environment variable %QT_PLUGIN_PATH% and put qsqlmysql.dll into %QT_PLUGIN_PATH%/sqldrivers/ . You can even do it in your Python script before invocation of QSqlDatabase.addDatabase :

os.environ['QT_PLUGIN_PATH'] = r'C:\projects\my-project-1\qt-plugins'

Note, qsqlmysql.dll must be a release version built using MSVC (64-bit since it is year 2022), not MinGW. Debug version fails by some reason in my experience.

If you don't want to define the %QT_PLUGIN_PATH% environment variable, an alternative fix is to copy qsqlmysql.dll into one of these directories: <python-install-dir>/sqldrivers/ or <python-install-dir>/lib/site-packages/PySide6/plugins/sqldrivers/ .

Another alternative is to use QCoreApplication.addLibraryPath like this:

    app = QCoreApplication(sys.argv)
    app.addLibraryPath(r'C:\projects\my-project-1\qt-plugins')

And yet another alternative is to create <python-install-dir>\qt.conf or <python-install-dir>\qt6.conf with following content:

[Paths]
Prefix=C:/projects/my-project-1
Plugins=qt-plugins

or even so:

[Paths]
Plugins=C:/projects/my-project-1/qt-plugins

NB qt6.conf is ignored if qt.conf doesn't exist. If you use qt6.conf , you must create an empty qt.conf at least.

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CASE #2: you execute QSqlDatabase.addDatabase("QMYSQL") , but you get the following error:

QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers: QMARIADB QMYSQL QSQLITE QODBC QPSQL

It means that qsqlmysql.dll was found, but its dependencies were not . The qsqlmysql.dll additionally requires 3 DLLs: libmysql.dll , libcrypto-1_1-x64.dll , libssl-1_1-x64.dll . These DLLs must be located in %PATH% or in current directory.

NB if you place the DLLs near your python script, this won't work if current working directory is different from scripts's location. But you can modify %PATH% even in your Python script. For example, if you copied said DLLs into deps sub-directory of your project:

os.environ["PATH"] += os.pathsep + os.path.join(os.path.dirname(__file__), 'deps')

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Another possible issues might be:

• architecture mismatch (some DLLs are 64-bit, while others are 32-bit).
• binary incompatibility - eg if "sqldrivers/qsqlmysql.dll" is built with MinGW or it's a debug version downloaded from https://github.com/thecodemonkey86/

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Define the environment variable: set QT_DEBUG_PLUGINS=1 - this might help to troubleshoot such issues.