code: def _get_db_fields(self, obj):
          
          for field in obj.indexes:
              yield field, self._zeo_key(field)
docs: Return list of database dictionaries, which are used as indexes for
          each attributes.
  
          Args:
              cached (bool, default True): Use cached connection to database.
  
          Returns:
              list: List of OOBTree's for each item in :attr:`.COMMON_FIELDS`.