Qt C++ Make QSqlDatabase static inside class

Question

I'm trying to implement a single QSqlDatabase instance for all instances of my class.

#include <QCoreApplication>
#include <QtSql/QSqlDatabase>

class MyClass
{
    static QSqlDatabase db;
};

QSqlDatabase MyClass::db = QSqlDatabase::addDatabase("QSQLITE");

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    return a.exec();
}

But this code doesn't seems to work in Release mode:

QSqlDatabase: an instance of QCoreApplication is required for loading driver plugins

Screen (error)
I've used windeployqt.exe to build independent Release version.

In Debug this works because sqldriver loaded directly from Qt directory. When i'm trying to put it to release it makes no sense.

Answer 1

QSqlDatabase: an instance of QCoreApplication is required for loading driver plugins

So you're not allowed to load sql plugins on the global level. Just don't try to make it "static inside class", but make it "static inside static method", like in a typical singleton pattern. Sort of,

class MyClass
{
    static QSqlDatabase& get_db();
};

QSqlDatabase& MyClass::get_db()
{
    static QSqlDatabase db;
    if (!db.isValid())
        db = QSqlDatabase::addDatabase("QSQLITE");
    return db;
}