.net - NHibernate select query -

i have following problem:

public ilist<category> getleafcategories() {     // select categories not parentcategory     string sqlquery =  @"     select * catalog_categories c     c.categoryid not in (         select distinct parentcategoryid          catalog_categories)     ";      //     // need equivalent nhibernate query     //     var categs = nhibernatesession.current.query<category>();     iqueryable<category> leafcategs = cat in categs                                       cat.id not in // how to???                                           (from c in categs                                             select c.parentcategory.id)                                         select cat;     return leafcategs.tolist(); } 

im not tested this, should work:

var session = nhibernatesession.current;  var subquery = session.query<category>     .select(x => x.parentcategory.id);  return session.query<category>     .where(x => !subquery.contains(x.id))     .tolist();