LINQ left join (转)

var q =
                (from ar in db.Articles
                 join c in db.Categories on ar.ParentId
                     equals c.Id
                 join sc in db.Categories on ar.SubId equals sc.Id into scate
                 from sc in scate.DefaultIfEmpty()
                 where ar.IsPrivate == false
                 orderby ar.CreateTime descending
                 __select new
                            {
                               article = ar,
                               pcate = c,
                               scate = sc