[Answer]-Cannot convert <QueryDict: {u..to decimal after limiting foreign key

Solved. The prob was in the call of my modelForm’s initialization.
Instead of the ‘expected’: form = MyForm(request.POST, own_instance.id)
tried form = MyForm(data=request.POST, own_id=own_instance.id), and it worked
because there is a distinction between positional and keyword arguments as I finally discovered.