docs: def save_model(self, request, obj, form, change):
          """Add an ObjectPosition to the object."""
          super(GenericPositionsAdmin, self).save_model(request, obj, form,
                                                        change)
          c_type = ContentType.objects.get_for_model(obj)
          try:
              ObjectPosition.objects.get(content_type__pk=c_type.id,
                                         object_id=obj.id)
          except ObjectPosition.DoesNotExist:
              position_objects = ObjectPosition.objects.filter(
                  content_type__pk=c_type.id, position__isnull=False).order_by(
                      '-position')
              try:
                  position = (position_objects[0].position + 1)
              except IndexError:
                  position = 1
              ObjectPosition.objects.create(
                  content_object=obj, position=position)