docs: def mapping(self):
          """Get a mapping class for this model
  
          This method will return a Mapping class for your model, generating it using settings from a
          `Mapping` class on your model (if one exists). The generated class is cached on the manager.
          """
          if not hasattr(self, "_mapping"):
              if hasattr(self.model, "Mapping"):
                  mapping_klass = type("Mapping", (DjangoMapping, self.model.Mapping), {})
              else:
                  mapping_klass = get_first_mapping(self.model)
                  if mapping_klass is None:
                      mapping_klass = DjangoMapping
              self._mapping = mapping_klass(self.model)
          return self._mapping