Ok, so its time to answer own question. The approach I used was incorrect and the problem can be solved much easier:
Qt generates QtQuick2ApplicationViewer class to handle main qml loading. Inside this class you can find a private function "adjustPath()". This function do exactly what we need - maps your local path to resources to global platform-dependent path. In order to use the function I maded it publicly visible and use it in form:
QString DatabaseManager::assetsPath()
{
return m_Viewer.adjustPath("database");
}
Thats it.