Question

我正在尝试将此sql转换为linq：

SELECT [t0].[ThreadId] FROM [MessageParticipants] AS [t0]
WHERE EXISTS(
  SELECT threadId
  FROM [MessageParticipants] AS [t1]
  WHERE ([t1].[UserId] = 23) 
) 
AND ([t0].[UserId] = 3)

我尝试过使用LINQPad进行转换，但我无法使用它

这几乎可以工作：

var result = from mp2 in MessageParticipants 
            let x = (from mp in MessageParticipants where mp.UserId == 3 select mp.UserId)
where  x.Contains(23)
select mp2;

result.Dump();

以上LINQ的结果查询（这是错误的）

DECLARE @p0 Int = 23
DECLARE @p1 Int = 3
SELECT [t0].[Id], [t0].[ThreadId], [t0].[UserId], [t0].[CreatedDate], [t0].[MessageId]
FROM [MessageParticipants] AS [t0]
WHERE EXISTS(
  SELECT NULL AS [EMPTY]
  FROM [MessageParticipants] AS [t1]
  WHERE ([t1].[UserId] = @p0) AND ([t1].[UserId] = @p1)
) --> AND should be here not in the inner query

也许有更好的方法？

我试图找到用户23和用户3是否已经通过查找threadId进行了持续对话。

所以MessageParticipants表看起来像这样：

Id, ThreadId, UserId
--------------------
1    52        23
2    52        3
3    11        20

Answer 1

我相信你的sql有点关闭，你应该在表上使用连接到自己，然后使用where为id。这是更新的sql，并在相应的linq下面获取线程ID。

-- create in memory table for testing
DECLARE @MessageParticipants table (Id INT identity, ThreadId int, UserId int)
insert into @MessageParticipants(ThreadId, UserId) values (52,23), (52,3), (11, 20),(11, 3)

SELECT [t0].[ThreadId]
FROM @MessageParticipants AS [t0]
INNER JOIN @MessageParticipants AS [t1] ON t0.ThreadId = t1.ThreadId
WHERE [t1].[UserId] = 3 AND [t0].[UserId] = 23

Linq声明

var result = from m1 in MessageParticipants
    join m2 in MessageParticipants on m1.ThreadId equals m2.ThreadId
    where m2.UserId == 3 && m1.UserId == 23
    select m1.ThreadId;

var thread = result.FirstOrDefault();

尝试使用子查询将sql转换为linq

1 个答案: