Question

我试图将SQL查询转换为linq，但不知道如何在连接语句中使用AND子句，就像我在此示例SQL Query中一样。

我已经突出了我在下面无法弄清楚的部分。

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
}

但使用WHERE会删除数据。

Answer 1

您可以将GroupId条件嵌入查询中：

 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
 }

Answer 2

这是您在多个列上进行联接的方式：

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
}

如何在LINQ join中使用AND

2 个答案: