code: def update_registered_subject_from_model_on_post_save(sender, instance, raw, created, using, **kwargs):
      
      if not raw and not kwargs.get('update_fields'):
          try:
              instance.registration_update_or_create()
          except AttributeError as e:
              if 'registration_update_or_create' not in str(e):
                  raise AttributeError(str(e))
docs: Updates RegisteredSubject from models using UpdatesOrCreatesRegistrationModelMixin.