code: def related_schema(self):
          
          relationship_field = self.name
  
          if relationship_field not in get_relationships(self.schema):
              raise InvalidFilters("{} has no relationship attribute {}".format(self.schema.__name__, relationship_field))
  
          return self.schema._declared_fields[relationship_field].schema.__class__
docs: Get the related schema of a relationship field
  
          :return Schema: the related schema