docs: def _set_up_reference_fields(new_class):
          """Walk through relation fields and setup shadow attributes"""
          if new_class.meta_.declared_fields:
              for _, field in new_class.meta_.declared_fields.items():
                  if isinstance(field, Reference):
                      shadow_field_name, shadow_field = field.get_shadow_field()
                      setattr(new_class, shadow_field_name, shadow_field)
                      shadow_field.__set_name__(new_class, shadow_field_name)