code: def keys(self, **kwargs):
          
          warnings.warn('Use of `rel.fetch.keys()` notation is deprecated. '
                        'Please use `rel.fetch("KEY")` or `rel.fetch(dj.key)` for equivalent result', stacklevel=2)
          yield from self._expression.proj().fetch(as_dict=True, **kwargs)
docs: DEPRECATED
          Iterator that returns primary keys as a sequence of dicts.