how to use letf outer join in LINQ

var query=
                from _t in db.E_Cat
                join _s in db.E_StoryDetail on _t.CatID equals _s.SCat into testSubject
                      from _s in testSubject.DefaultIfEmpty()
                    group _t by new {_t.CatID,_t.CatName} into g
                select new { CatID = g.Key.CatID, CatName=g.Key.CatName, count = g.Count() };