Question

如何将下面的sql更改为linq。

select distinct * from dbo.TbleA a
left outer join dbo.TbleB b on a.schid = b.schid
left outer join dbo.TbleC c on b.addrid=c.addrid
and c.userid=a.userid
where b.addrid=1

这是我的linq版本导致错误：

from a in db.TbleA
join b in db.TbleB on a.schid equals b.schid
join c in db.TbleC on new { w = b.addrid, z = a.userid } equals new { w=(int?)c.addrid, z=c.userid}
where (b.addrid == 1)

我在这里遇到错误：

在新的{w = b.addrid，z = a.userid}等于new {{ w =（int？）c.addrid，z = c.userid}

我确实理解问题出在哪里我与我的联盟中的两个表进行比较。谢谢，错误是：

＆＃34; join子句中某个表达式的类型不正确＆＃34;＆＃34;在加入调用中类型推断失败＆＃34;

b.addrid - int, 
a.userid - string, 
c.addrid - int?
c.userid - string

Answer 1

我们无法在不知道所涉及的类型的情况下，在编译方面真正说出您当前查询的错误，但它无论如何都不会等同于原始SQL，因为您想要离开外连接。我怀疑你想要更像的东西：

from a in db.TbleA
join b in db.TbleB on a.schid equals b.schid into bs
from b in bs.DefaultIfEmpty()
join c in db.TbleC on new { w = (int?)b?.addrid, z = a.userid }
               equals new { w = c.addrid, z = c.userid } into cs
from c in cs.DefaultIfEmpty()
where (b.addrid == 1)

如果你可以将C＃6与null条件运算符一起使用，那当然。如果没有，您至少逻辑上需要：

from a in db.TbleA
join b in db.TbleB on a.schid equals b.schid into bs
from b in bs.DefaultIfEmpty()
join c in db.TbleC on new { w = (b == null ? default(int?) : (int?)b.addrid), z = a.userid }
               equals new { w = c.addrid, z = c.userid } into cs
from c in cs.DefaultIfEmpty()
where b == null || b.addrid == 1

Answer 2

我怀疑您的错误是由于尝试比较LinQ语句中不同类型的匿名类而引起的。我建议你将联接更改为以下内容：

from a in db.TbleA
join b in db.TbleB on a.schid equals b.schid
join c in db.TbleC on new { w = (int?)b.addrid, z = a.userid } equals new { w=(int?)c.addrid, z=c.userid}
where (b.addrid == 1)

多条连接条件sql到linq

2 个答案: