code: public void _orderByDescending(String field, OrderingType ordering) {
          assertNoRawQuery();
          String f = ensureValidFieldName(field, false);
          orderByTokens.add(OrderByToken.createDescending(f, ordering));
      }
docs: Order the results by the specified fields
  The fields are the names of the fields to sort, defaulting to sorting by descending.
  You can prefix a field name with '-' to indicate sorting by descending or '+' to sort by ascending
  @param field Field to use
  @param ordering Ordering type