Question

我有3个名为Player，PlayerDetails和Team的表。我想写一个linq语句，如

from p in Player join d in PlayerDetails on p.ID equals d.PID

然后右键加入团队表，Player有一个名为TID的列，它面向Team表的ID。

我试图写一个像

这样的陈述

from p in Player join d in PlayerDetails on p.ID equals d.PID into PlayerGroup
from t in team join g in PlayerGroup on t.ID equals g.p.ID

当然无法奏效。我不确定如何编写这种类型的查询语句，表左连接表2然后右连接表3。

谁可以提供帮助？

Answer 1

我相信你可以这样做：

var LeftJoin =
    from p in Player
    join d in PlayerDetails on p.ID equals d.PID into pd
    from d in pd.DefaultIfEmpty()
    select new
    {
        pID = p.ID,
        pTID = p.TID,
        dID = d.ID
    };

var RightJoin =
    from t in Team
    join l in LeftJoin on t.ID equals l.pTID into tl
    from l in tl.DefaultIfEmpty()
    select new
    {
        tID = t.ID,
        pID = l.pID,
        pTID = l.PTID,
        dID = l.dID
    };

要在一个查询中执行所有操作，我认为您可以（不测试）执行以下操作：

var RightJoin =
    from t in Team
    join l in
        (from p in Player
         join d in PlayerDetails on p.ID equals d.PID into pd
         from d in pd.DefaultIfEmpty()
         select new
         {
             pID = p.ID,
             pTID = p.TID,
             dID = d.ID
         })
    on t.ID equals l.pTID into tl
    from l in tl.DefaultIfEmpty()
    select new
    {
        tID = t.ID,
        pID = l.pID,
        pTID = l.PTID,
        dID = l.dID
    };

Linq加入多个表

1 个答案: