linq to sql多表级联查询,该如何解决

linq to sql多表级联查询
有个表A，表B，表C。A里面是sid,pid,username.B里面是sname,c里面是pname。要求级联查询出sname,pname新手刚接触linq求指导。

[解决办法]

C# code

var linq=from a in A         from b in B         from c in C         where a.sid=b.id and a.pid=c.id         select new{           b.sname,           c.pname          }
[解决办法]
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引用:

C# code

var linq=from a in A
from b in B
from c in C
where a.sid=b.id and a.pid=c.id
select new{
b.sname,
c.pname
}


那个大写的A,B,C是一个临时变量还是？？

[解决办法]
C# code
var linq=from a in A join b in B on a.sid=b.id                     join c in C on a.pid=c.id         select new{           b.sname,           c.pname          }
[解决办法]
C# code
    public class _2011_12_12_01 : TestUnit    {        public override void Run()        {            var a = new List<A>();            var b = new List<B>();            var c = new List<C>();            a.Add(new A { sid = 1, pid = 1, username = "u1" });            a.Add(new A { sid = 2, pid = 2, username = "u2" });            a.Add(new A { sid = 3, pid = 3, username = "u3" });            b.Add(new B { sid = 1, sname = "s1" });            b.Add(new B { sid = 2, sname = "s2" });            b.Add(new B { sid = 3, sname = "s3" });            c.Add(new C { pid = 1, pname = "p1" });            c.Add(new C { pid = 2, pname = "p2" });            c.Add(new C { pid = 3, pname = "p3" });            var results = a.Join(                b,                xa => xa.sid,                xb => xb.sid,                (xa, xb) => new { username = xa.username, sname = xb.sname, pid = xa.pid }                ).Join(                c,                xa => xa.pid,                xc => xc.pid,                (xa, xc) => new { username = xa.username, sname = xa.sname, pname = xc.pname });            foreach (var item in results) {                Console.WriteLine("{0,10}{1,10}{2,10}", item.username, item.sname, item.pname);            }        }    }    class A    {        public int sid { get; set; }        public int pid { get; set; }        public string username { get; set; }    }    class B    {        public int sid { get; set; }        public string sname { get; set; }    }    class C    {        public int pid { get; set; }        public string pname { get; set; }    }
[解决办法]
探讨

C# code

var linq=from a in A
         from b in B
         from c in C
         where a.sid=b.id and a.pid=c.id
         select new{
           b.sname,
           c.pname
          }

[解决办法]
那就对B连两次
C# code
            results = a.Join(                b,                xa => xa.sid,                xb => xb.vid,                (xa, xb) => new { username = xa.username, sname = xb.name, pid = xa.pid }                ).Join(                b,                xa => xa.pid,                xb => xb.vid,                (xa, xb) => new { username = xa.username, sname = xa.sname, pname = xb.name}                );