Link problems with static MySQL plugin

[wysota]

Your Qt is compiled in shared mode, so you can't use static plugins. You have to use regular plugins. First verify if you have them in your sqldrivers directory. If so, check if you have libmysqlclient installed as the driver won't work without it.

[nurtsi]

I have the plugin:

$ ls /usr/lib/qt4/plugins/sqldrivers/
libqsqlmysql.so

$ ls /usr/lib/qt4/plugins/sqldrivers/
libqsqlmysql.so

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And I have libmysqlclient:

$ ls /usr/lib/libmysqlclient*
/usr/lib/libmysqlclient.so     /usr/lib/libmysqlclient.so.15.0    /usr/lib/libmysqlclient_r.so     /usr/lib/libmysqlclient_r.so.15.0
/usr/lib/libmysqlclient.so.15  /usr/lib/libmysqlclient.so.15.0.0  /usr/lib/libmysqlclient_r.so.15  /usr/lib/libmysqlclient_r.so.15.0.0

$ ls /usr/lib/libmysqlclient*
/usr/lib/libmysqlclient.so     /usr/lib/libmysqlclient.so.15.0    /usr/lib/libmysqlclient_r.so     /usr/lib/libmysqlclient_r.so.15.0
/usr/lib/libmysqlclient.so.15  /usr/lib/libmysqlclient.so.15.0.0  /usr/lib/libmysqlclient_r.so.15  /usr/lib/libmysqlclient_r.so.15.0.0

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I re-read the plugins-howto and found some stuff I missed earlier. Do I actually need to load the plugin manually (instead of just linking against it) with QPluginLoader by declaring an interface and writing some wrapper class to it?

I made this very simple test which I want to get working.

Test.cpp:

#include <QSqlDatabase>
 
int main(int argc, char** argv)
{
  QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
  return 0;
}

#include <QSqlDatabase>

int main(int argc, char** argv)
{
  QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
  return 0;
}

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Test.pro:

SOURCES += Test.cpp
QT = sql
QTPLUGIN = qsqlmysql
TARGET = test

SOURCES += Test.cpp
QT = sql
QTPLUGIN = qsqlmysql
TARGET = test

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It compiles fine but I run it and it doesn't find any SQL drivers:

$ ./test
QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers:

$ ./test
QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers:

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[nurtsi]

I actually managed to get it working. Apparently you need to instantiate QApplication (or in this case QCoreApplication) which actually loads the plugins. Nothing in the plugin documentation explicitly states this, but anyhow this works:

#include <QSqlDatabase>
#include <QCoreApplication>
 
int main(int argc, char** argv)
{
  QCoreApplication app(argc, argv);
 
  QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
 
  return 0;
}

#include <QSqlDatabase>
#include <QCoreApplication>

int main(int argc, char** argv)
{
  QCoreApplication app(argc, argv);

  QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");

  return 0;
}

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[wysota]

Yes, plugins are loaded in QCoreApplication constructor (I must have missed the lack of QApplication in your previous code, sorry). By the way ".so" is a shared object, not a static plugin, therefore you're using real plugins, not static ones now.