Propel：orderby与useTableQuery中的列

I have following query:

$ratings = RatingQuery::create()
          ->useProductsQuery('a', 'left join') 
              ->filterByProductName('%'.trim($_REQUEST['title']).'%', Criteria::LIKE) 
          ->endUse()
          ->groupByRatingModel()
          ->orderByRatingTimestamp('desc')
          ->find();

By default it is ordered by ratingTimeStamp-desc. I want to order it by productName-asc

I tried to change the order in useProductsQuery, but is does not work. Any ideas?

VEry simple :-)

$ratings = RatingQuery::create()
          ->useProductsQuery('a', 'left join') 
              ->filterByProductName('%'.trim($_REQUEST['title']).'%', Criteria::LIKE) 
              ->orderByProductName('asc')
          ->endUse()
          ->groupByRatingModel()
       // ->orderByRatingTimestamp('desc')
          ->find();