docs: def get_mapping(self, meta_fields=True):
          '''
          Returns the mapping for the index as a dictionary.
  
          :param meta_fields: Also include elasticsearch meta fields in the dictionary.
          :return: a dictionary which can be used to generate the elasticsearch index mapping for this doctype.
          '''
          return {'properties': dict((name, field.json()) for name, field in iteritems(self.fields) if meta_fields or name not in AbstractField.meta_fields)}