broker.getDescriptorRepository().setClassDescriptor(cldProductGroup);
broker.getDescriptorRepository().setClassDescriptor(cldArticle);
Criteria crit = new Criteria();
crit.addNotNull("productGroupId");
crit.addLessOrEqualThan("productGroupId", new Integer(5));
QueryByCriteria q = QueryFactory.newQuery(Article.class, crit);
q.addOrderByDescending("productGroupId");
q.addPrefetchedRelationship("productGroup");
Collection results = broker.getCollectionByQuery(q);