实体框架和linq查询构建

Question

我想知道是否有更好的方法来构造我的linq查询（我使用EF CodeFirst）来访问我的表。眼下，它产生以下查询：

exec sp_executesql N'SELECT 
[Project4].[Id] AS [Id], 
[Project4].[First] AS [First], 
[Project4].[Last] AS [Last], 
[Project4].[Email] AS [Email] 
FROM (SELECT 
    [Project3].[Id] AS [Id], 
    [Project3].[First] AS [First], 
    [Project3].[Last] AS [Last], 
    [Project3].[Email] AS [Email], 
    CASE WHEN ([Extent5].[Id] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1] 
    FROM (SELECT 
     [Project2].[Id] AS [Id], 
     [Project2].[First] AS [First], 
     [Project2].[Last] AS [Last], 
     [Project2].[Email] AS [Email] 
     (SELECT 
      SUM([Extent4].[Data]) AS [A1] 
      FROM [dbo].[EventHistory] AS [Extent4] 
      WHERE [Project2].[Id] = [Extent4].[UserId]) AS [C1] 
     FROM (SELECT 
      [Extent1].[Id] AS [Id], 
      [Extent1].[First] AS [First], 
      [Extent1].[Last] AS [Last], 
      [Extent1].[Email] AS [Email] 
      (SELECT 
       SUM([Extent3].[Data]) AS [A1] 
       FROM [dbo].[EventHistory] AS [Extent3] 
       WHERE [Extent1].[Id] = [Extent3].[UserId]) AS [C1] 
      FROM [dbo].[User] AS [Extent1] 
      WHERE (EXISTS (SELECT 
       1 AS [C1] 
       FROM [dbo].[EventHistory] AS [Extent2] 
       WHERE [Extent1].[Id] = [Extent2].[UserId] 
      )) AND ([Extent1].[Id] = @p__linq__0) 
     ) AS [Project2] 
     WHERE [Project2].[C1] >= @p__linq__1) AS [Project3] 
    LEFT OUTER JOIN [dbo].[EventHistory] AS [Extent5] ON [Project3].[Id] = [Extent5]. [UserId] 
    WHERE [Project3].[C1] <= @p__linq__2 
) AS [Project4] 
ORDER BY [Project4].[Id] ASC, [Project4].[C1] ASC',N'@p__linq__0 int,@p__linq__1 int,@p__linq__2 int',@p__linq__0=1717,@p__linq__1=300,@p__linq__2=400 

...这似乎是相当可怕的我，为什么它会创建所有这些不同的子选择？ - 对我来说，它真的应该产生类似于：

选择u.id，第一个，最后一个，电子邮件，e。*从用户u 左加入eventhistory e上e.userid = u.id和e.data < = @参数1和e.data> = @参数2 和u.id = @id

我的代码看起来是这样的：

IQueryable<User> query = from users in this.DataContext.Users.Include("EventHistoryList") 
           where users.EventHistoryList.Any() 
           select users; 

     if (playerId.HasValue) 
      query = query.Where(u => u.Id == playerId.Value); 

     if (dataLow.HasValue) 
      query = query.Where(u => u.EventHistoryList.Sum(p => p.Data) >= dataLow.Value); 

     if (dataHigh.HasValue) 
      query = query.Where(u => u.EventHistoryList.Sum(p => p.Data) <= dataHigh.Value); 

query = query.OrderByDescending(orderBy).Skip(startEntity).Take(pageSize).ToList(); 

任何帮助，将不胜感激。谢谢！

Answer 1

它看起来像一个子选择处理分页，其他的是必要的，因为你正在对具有0 .. *关系的表应用聚合函数。我确信查询可以看起来更好，但我不认为这是不必要的低效率。

您认为应该生成的查询将从数据库中抓取整个结果集，并且还需要使用子查询来应用聚合函数。从数据库获取整个结果集并在之后进行分页将是非常低效的。