code: def _field_is_pk(self, field_name):
          
          if self.cls._field_is_pk(field_name):
              return True
          if field_name.endswith('__eq') and self.cls._field_is_pk(field_name[:-4]):
              return True
          return False
docs: Check if the given name is the pk field, suffixed or not with "__eq"