def apply_field_limits(self, fields={}, exclude_fields={}):
        for collection_name, flds in exclude_fields.items():
            qs = self._querysets[collection_name].exclude(*flds)
            self._querysets[collection_name] = qs

        for collection_name, flds in fields.items():
            qs = self._querysets[collection_name].only(*flds)
            self._querysets[collection_name] = qs
Limit the fields returned when evaluating the querysets.
dataset/ETHPy150Open openelections/openelections-core/openelex/base/bake.py/Roller.apply_field_limits