问题在最后。IEnumerable属性聚合/连接的具体化和性能
这里是
public class Head {
public Int32 Id {get; set;}
public virtual ICollection<Detail> Details {get; set;}
}
public class Detail {
public Int32 Id {get; set;}
public virtual Head Head {get; set;}
public Int32 IType {get; set;}
public String Code {get; set;}
}
我需要的是填补了网格至少两列的情况:
- Head.Id
- 级联码值用于表示头部和一给出Detail.Type值。
我第一次尝试是:
Int32 givenValue = 2;
var q = repo.Heads.
Where(w.Expand()).
Select(x => new {
Id = x.IdFolder,
Details = x.Details.Select(y => new {
Id = y.Id,
IType = y.IType,
Code = y.Name
})
}).OrderBy(x => x.Id).Take(taked).
ToList(). // One hit to the database
Select(y => new {
Id = y.Id,
Codes2AsString = String.Join(
",",
y.Details.Where(z => z.IType == givenValue).Select(z => z.Code))
}).
ToList();
它工作正常。 (我知道我应该过滤数据库端的细节,但我需要整套其他连接。)
但是:这段代码慢了8到10,相当于Linq到SQL(我正在迁移现有的应用程序)为2850头。这需要4到5秒才能填满网格,而不是接近0秒。
我的第二次尝试是在数据库端进行聚合/连接,就像在旧版本的应用程序中一样。
我创建一个视图(用TSQL特异性)
create view as v_Head2Codes
select
h.Id,
(
select ',' + id.Code as [text()]
from
Details id
Where
id.Header_Id == h.Id and id.IType = 2
order by id.Code
For XML PATH ('')
) Codes
from
Headers h
然后创建一个新的类
public class VHead2Codes {
public Int32 Id {get; set;}
public String Codes {get; set;}
}
我这个新类映射到视图和修改我的头班
public class Head {
public Int32 Id {get; set;}
public virtual ICollection<Detail> Details {get; set;}
public virtual VHead2Codes Codes2AsString {get; set;}
}
我设置了一对一的关系,我的查询变成了
var q = repo.Heads.
Where(w.Expand()).
Select(x => new {
Id = x.IdFolder,
Codes2AsString = x.Codes2AsString.Codes
}).OrderBy(x => x.Id).Take(taked).
ToList(); // One hit to the database
这里我得到了和以前一样的结果和相同的性能。
我的第一个猜测是EF实现过程使用了丢失的微处理器周期。 但它可能是错误的(请参阅第二条评论)。循环在串联:循环遍历头部和细节上丢失。
我的问题是:有没有另一种方式允许通过保持perfs来避免视图?
============================================== =======================
=======对您的请求,生成的SQL ========= =================
LINQ查询是:
Folders.Select(x => new {
Id = x.IdFolder,
Contribs = x.Contributors.Select(y => new {
Name = y.Contributor.LastName
})
})
的SQL:
SELECT
[Project1].[idDossier] AS [idDossier],
[Project1].[C1] AS [C1],
[Project1].[ThirdParty_Id] AS [ThirdParty_Id],
[Project1].[LastName] AS [LastName]
FROM (SELECT
[Extent1].[idDossier] AS [idDossier],
[Join1].[ThirdParty_Id] AS [ThirdParty_Id],
[Join1].[LastName] AS [LastName],
CASE WHEN ([Join1].[ThirdParty_Id] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]
FROM [dbo].[tableD] AS [Extent1]
LEFT OUTER JOIN (SELECT [Extent2].[ThirdParty_Id] AS [ThirdParty_Id], [Extent2].[TableD_Id] AS [TableD_Id], [Extent3].[LastName] AS [LastName]
FROM [dbo].[FolderContributions] AS [Extent2]
INNER JOIN [dbo].[v_ThirdParties] AS [Extent3] ON ([Extent2].[ThirdParty_Id] = [Extent3].[Id]) AND ([Extent2].[ThirdParty_Source] = [Extent3].[Source])) AS [Join1] ON [Extent1].[idDossier] = [Join1].[TableD_Id]
) AS [Project1]
ORDER BY [Project1].[idDossier] ASC, [Project1].[C1] ASC
你比较了产生查询(通过L2S和EF)? – Maarten 2014-10-22 09:11:55
@Maarten老实说,我只是检查一下EF是否只打了一次数据库。但是L2S版本使用了与该视图等价的功能,并且SSMS中的EF sql查询执行时间不到0秒。我通过去除串联(将Codes2AsString设置为“”)来测试,并且网格填充速度更快。 – tschmit007 2014-10-22 09:20:13
你确定Codes2AsString计算不会发出子选择又名SELECT N + 1吗? – Firo 2014-10-22 09:39:42