在 Entity Framework 中，如何用 LInq 表达式生成带聚合函数的 SQL，同时分组以及排序

先给大家说一下我的需求。

我要生成的 SQL 语句如下：

select r.UserID, r.UserName, max(StudentPoint) as ResultStudentPoint, max(CreateTime) as ResultCreateTime  from CR_UserRecite r
where PaperId='90F8533E-B2E0-42E2-8122-3A3FE3DDB49B'
group by r.UserID,r.UserName order by ResultStudentPoint desc, ResultCreateTime desc

其中 PaperID 是需要动态查询了，这里为了演示就写死了。

经过在 Entity Framework 4.1 Code First 中尝试，写出如下的代码，满足了需求。

// 其中 context 是 System.Data.Entity.DbContext 的类， TodayRank 是自己定义的类型
// 下面代码是意思就是搜索特定 PagerID 的 UserRecite ，根据 r.UserID, r.UserName 分组，取每个人的最高分，根据最高分（降序）和时间（降序）排序
IQueryable<TodayRank> query = from r in context.UserRecites
where r.PaperID == new Guid("90f8533e-b2e0-42e2-8122-3a3fe3ddb49b&a=1")
group r by new { r.UserID, r.UserName } into result
let scoreMax = result.Max(n => n.StudentPoint)
let createdTimeMax = result.Max(n => n.CreateTime)
orderby scoreMax descending, createdTimeMax descending
select new TodayRank()
{
UserID = result.Key.UserID,
UserName = result.Key.UserName,
Score = scoreMax,
CreateTime = createdTimeMax
};
List<TodayRank> ltTodayRanks = query.Take(10).ToList();

最后生成的 SQL 基本上也是满足需求的，只是代码比较多！

看来 EF 还蛮够智能的，赞！

exec sp_executesql N'SELECT TOP (10)
[Project3].[UserID] AS [UserID],
[Project3].[UserName] AS [UserName],
[Project3].[C2] AS [C1],
[Project3].[C3] AS [C2]
FROM
(
SELECT
[Project2].[C1] AS [C1],
[Project2].[UserID] AS [UserID],
[Project2].[UserName] AS [UserName],
CAST( [Project2].[C1] AS decimal(19,0)) AS [C2],
[Project2].[C2] AS [C3]
FROM
(
SELECT
[Project1].[C1] AS [C1],
[Project1].[UserID] AS [UserID],
[Project1].[UserName] AS [UserName],
(
SELECT
MAX( [Extent2].[CreateTime] ) AS [A1]
FROM [dbo].[CR_UserRecite] AS [Extent2]
WHERE ( [Extent2].[PaperID] = @p__linq__0 ) AND
(
[Project1].[UserID] = [Extent2].[UserID]
)
AND
(
( [Project1].[UserName] = [Extent2].[UserName] )
OR
(
( [Project1].[UserName] IS NULL )
AND ( [Extent2].[UserName] IS NULL )
)
)
) AS [C2]
FROM
(
SELECT
[GroupBy1].[A1] AS [C1],
[GroupBy1].[K1] AS [UserID],
[GroupBy1].[K2] AS [UserName]
FROM
(
SELECT
[Extent1].[UserID] AS [K1],
[Extent1].[UserName] AS [K2],
MAX( [Extent1].[StudentPoint] ) AS [A1]
FROM [dbo].[CR_UserRecite] AS [Extent1]
WHERE [Extent1].[PaperID] = @p__linq__0
GROUP BY [Extent1].[UserID], [Extent1].[UserName]
)
AS [GroupBy1]

)
AS [Project1]
)
AS [Project2]
)
AS [Project3]
ORDER BY [Project3].[C1] DESC,
[Project3].[C3] DESC',N'@p__linq__0 uniqueidentifier',@p__linq__0='90F8533E-B2E0-42E2-8122-3A3FE3DDB49B'

谢谢浏览！