Sql 不在 LINQ 查询的子查询子句中的查询

Question

   select * from user_user_connection 
where userid_from = 3464 and 
userid_to not in
(select userid_from from 
user_user_connection 
where userid_to = 3464);

大家好，我是 entity framework 的新手。我正在尝试将此查询转换为 LINQ 查询，但无法理解如何使用 not in 子句编写子查询。另外，join 和 Include 哪个更好？

Answer 1

可能是这样的：

var list = userConnection.Where(user => user.useridto == 3464).Select(user => user.userid_from).ToList();
var list2 = userConnection.Where(user => !list.Contains(user.userid_to));

可能可以改进，因为包含需要相当长的时间（也许将列表放入哈希集中？）

Answer 2

这应该有效：

var query = 
   from uc in ctx.user_user_connection
   where uc.userid_from = 3464 && 
     !(from uc2 in ctx.user_user_connection
      where uc2.userid_to = 3464
      select uc2.userid_from).Contains(uc.userid_to)
   select uc;

或通过EXISTS

var query = 
   from uc in ctx.user_user_connection
   where uc.userid_from = 3464 && 
     !(from uc2 in ctx.user_user_connection
      where uc2.userid_to = 3464 && uc.userid_to == uc2.userid_from
      select uc2).Any()
   select uc;

Ov 通过 LEFT JOIN

var query = 
   from uc in ctx.user_user_connection
   from uc2 in ctx.user_user_connection
     .Where(uc2 => uc2.userid_from == 3464 && uc.userid_to == uc2.userid_from)
     .DefaultIfEmpty()
   where uc.userid_from = 3464 && uc2 == null
   select uc;

Answer 3

这个

    from a in user_user_connection 
    join b in user_user_connection on 
        new {From=a.userid_to, To=a.userid_from} equals new {From=b.userid_from, To=b.userid_to} into c
    from d in c.DefaultIfEmpty()
    where d == null
    select a;

类似于

select a.*
from user_user_connection a
left join user_user_connection b on a.userid_to = b.userid_from and a.userid_from = b.userid_to
where b.userid_from is null

这应该与您的未查询匹配。

如果你想要一个特定的 userid_from 你可以添加另一个 where

    from a in user_user_connection 
    where a.userid_from == 3464
    join b in user_user_connection on 
        new {From=a.userid_to, To=a.userid_from} equals new {From=b.userid_from, To=b.userid_to} into c
    from d in c.DefaultIfEmpty()
    where d == null
    select a;

Sql 不在 LINQ 查询的子查询子句中的查询

Sql Query with not in clause of subquery to LINQ query

c#

linq

entity-framework

sql-to-linq-conversion