problem with creating a query using criteria in nhibernate

I want to reproduce the following query using criteria:

select a.ID as article, count(c.ID) as commentsCount from Comments c left outer join Articles a on a.ID=c.ArticleID where a.ID in (2,10) group by a.ID 

I wrote it, but somewhere I must have an error, because the result is different than I expected.

The criteria:

ICriteria criteria = Session.CreateCriteria<Comment>("c") .CreateCriteria("Article", "a", NHibernate.SqlCommand.JoinType.LeftOuterJoin) .Add(Restrictions.In("a.ID", articleIDs)) .SetProjection(Projections.Property("a.ID")) .SetProjection(Projections.Count("c.ID")) .SetProjection(Projections.GroupProperty("a.ID")); 

NHibernate generates the following sql using this criteria:

SELECT a1_.ID as y0_ FROM Comments this_ left outer join Articles a1_ on this_.ArticleID = a1_.ID WHERE a1_.ID in (2 /* @p0 */,10 /* @p1 */) GROUP BY a1_.ID 

And the mapping:

public class Comment : EntityBase<int> { public virtual Article Article { set; get; } } public CommentMap() { Id(x => x.ID).GeneratedBy.Identity(); References(x => x.Article).Not.Nullable() .LazyLoad().Cascade .SaveUpdate().Column("ArticleID"); }