EF 左外连接查询数据

   //使用linq
   var database = from c in oaentities.Userchild
            join f in oaentities.Userfather on c.Fid equals f.Cid into leftjointemp
            from leftjoin in leftjointemp.DefaultIfEmpty()
            select new
            {
             c.sid,
             c.Username,
             leftjoin.Fathername
            };
      var joinfdatabase = database.ToList();

 var database = oaentities.Userchild.GroupJoin(oaentities.Userfather, a => a.Fid, b => b.Cid, (user, parent) => new
            {
                //主表字段可以点出来
                user = user,
                //附表字段不能点出来
                Father = parent
            }).SelectMany(a => a.Father.DefaultIfEmpty(), (last, parent) => new LeftJoinDatabeseController {
            //给需要显示的字段赋值（LeftJoinDatabeseController 类需要自己创建，需要显示的字段是这个类的成员）
            sid = last.user.sid,
            Username = last.user.Username,
            Fathername = parent.Fathername
            });
            //向前台输出
            ViewBag.joinfdatabase = database.ToList();