Linq左外连接 多字段连接

 1      var query =(from t1 in db.table1
 2                  join t2 in db.table2
 3                  on new {ID=t1.ID1,UserID=t1.ID2}
 4                  equal new {ID=t2.LID1,UserID=t2.LID2}
 5                  into temp
 6                  from t in temp.DefaultIfEmpty()
 7                  where t1.ID1=99
 8                  orderby t1.V1 descending
 9                  select new
10                  {
11                         t1.ID1,
12                         t1.ID2,
13                         t1.V1,
14                         t.V2 ??  0
15                  }).ToList();