如何在LINQ联接中使用AND

本文关键字：AND LINQ | 更新日期: 2023-09-27 18:24:42

我正在尝试将SQL查询转换为linq，但不知道如何像本例SQL query中那样在联接语句中使用AND子句。

我在下面强调了我无法理解的部分。

DECLARE @GroupId INT = 10
SELECT 
    U.UserName, 
    U.UserID, 
    @GroupId AS "GroupID", 
    CASE WHEN GU.GROUPID IS NULL THEN 0 
         ELSE 1 END 
         AS InGroup 
FROM Users U
LEFT JOIN GroupUsers GU on GU.UserID = U.UserID 
    AND GU.GROUPID = @GroupId -- HERE!!

这和我的一样接近

from user in Users
join gu in GroupUsers on user.UserID equals gu.UserID into subq
from sub in subq.DefaultIfEmpty()
where sub.GroupID == 10 || sub == null
select new
{
    Username = user.UserName,
    UserId = user.UserID,
    GroupId = 10,
    InGroup = sub != null
}

但是它使用CCD_ 1来移除数据。

如何在LINQ联接中使用AND

您可以将GroupId条件嵌入到查询中：

 from user in Users
 join gu in GroupUsers.Where(gu => gu.GroupID == 10)
    on user.UserID equals gu.UserID into subq
 from sub in subq.DefaultIfEmpty()
 select new 
 {
     Username = user.UserName,
     UserId = user.UserID,
     GroupId = 10,
     InGroup = sub != null
 }

这就是在多列上进行联接的方法：

from user in Users
join gu in GroupUsers on new { user.UserID, user.GroupID } equals new { gu.UserID, gu.GroupID } subq
from sub in subq.DefaultIfEmpty()
select new 
{
   Username = user.UserName,
   UserId = user.UserID,
   GroupId = sub == null ? null : sub.GroupID,
   InGroup = sub != null
}
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