Building QMYSQL / MARIADB with Qt 6.3.0

AnUnusualRemote

Something I didn't realise, when looking at Qt Creator, I was using a Replacement for Qt 6.2.3. This, along with receiving .dll files from a friend managed to output

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

When running my program using QMYSQL. Code below is how I'm designating QMYSQL as the driver used.

  QSqlDatabase database = QSqlDatabase::addDatabase("QMYSQL");
    database.setHostName("localhost");
    database.setDatabaseName("database_name");
    database.setUserName("username");
    database.setPassword("password");

So this means that either something is wrong with how I'm trying to load the QMYSQL driver, or there's something beyond this that could be preventing the driver from being loaded. Any ideas on what this could be?

SGaist

Hi and welcome to devnet,

If memory serves well, the online installer also provides the option to install cmake.

As for the loading issue, start your application with the QT_DEBUG_PLUGINS environment variable set to 1. You can do that in the Run part of the Project panel.

AnUnusualRemote

Sorry, I have done that correct, I just found it.
That doesn't seem to have done anything, in fact it was already set towards 1 when I checked. The online installer also seems to have CMake 3.21.1 64-bit showing as installed under Developer and Designer Tools.

SGaist

If the environment variable is properly defined, you should have a dump of information about the plugins being loaded and why they failed.

AnUnusualRemote

@SGaist
I'm assuming this would be

{
    "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
    "MetaData": {
        "Keys": [
            "QMYSQL",
            "QMARIADB"
        ]
    },
    "archlevel": 0,
    "className": "QMYSQLDriverPlugin",
    "debug": true,
    "version": 393728
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("QMYSQL", "QMARIADB")
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlodbc.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlodbc.dll, metadata=

Along with this line.

qt.core.library: "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlmysql.dll" cannot load: Cannot load library C:\Qt\6.3.0\mingw_64\plugins\sqldrivers\qsqlmysql.dll: The specified module could not be found.
qt.core.plugin.loader: QLibraryPrivate::loadPlugin failed on "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlmysql.dll" : "Cannot load library C:\\Qt\\6.3.0\\mingw_64\\plugins\\sqldrivers\\qsqlmysql.dll: The specified module could not be found."

sqldriver folder containing .dll files
Since that's the sqldriver folder, I checked. Results are above. I can only guess that there's a missing .debug file, or that the .dll is incompatible with Qt for some reason.

SGaist

Maybe a silly question but are you sure that the dll you have now is from the correct compiler ?

AnUnusualRemote

@SGaist
Very likely that it may not be from the right compiler, I could not compile it, so I asked a friend to instead. I suppose my best option right now is to try and build everything myself.

SGaist

You do not have to rebuild everything. Just the plugin.

AnUnusualRemote

@SGaist
I'm not entirely sure how to build it based on the documentation. I have the files for MariaDB location in the right folders when it comes to the .lib, .dll and .h files. Problem is that I'm not sure where I should be for building the plugins when it comes to the command prompt.

mkdir build-sqldrivers
cd build-sqldrivers

qt-cmake -G Ninja <qt_installation_path>\Src\qtbase\src\plugins\sqldrivers -DCMAKE_INSTALL_PREFIX=<qt_installation_path>\<platform> -DMySQL_INCLUDE_DIR="C:\mysql-8.0.22-winx64\include" -DMySQL_LIBRARY="C:\mysql-8.0.22-winx64\lib\libmysql.lib"
cmake --build .
cmake --install .

I'm not entirely sure where I should be located within my file structure to build the plugins, inside of the Qt 6.3.0 folder? The bin folder of the Qt 6.3.0 folder perhaps? qt-cmake doesn't seem to be recgonised as a command, so I assume it's located somewhere inside of the Qt folder.

'qt-cmake' is not recognized as an internal or external command, operable program or batch file.

I also do not know what Ninja refers to within the command. Do I need to install this too?

SGaist

Try with just cmake in place of qt-cmake.

As for Ninja, it's also available through the installer.

AnUnusualRemote

@SGaist
Since I'm using and building for MariaDB

qt-cmake -G Ninja <qt_installation_path>\Src\qtbase\src\plugins\sqldrivers -DCMAKE_INSTALL_PREFIX=<qt_installation_path>\<platform> -DMySQL_INCLUDE_DIR="C:\mysql-8.0.22-winx64\include" -DMySQL_LIBRARY="C:\mysql-8.0.22-winx64\lib\libmysql.lib"

The DMySQL and DMySQL_LIBRARY should probably be replaced with DMariaDB or some equivalent, correct? The locations will change, but obviously those are where I've installed the relevant files.

SGaist

From memory, no, MariaDB is a drop in replacement so it would not make sense to complicate the build system for that.