我必须对我的实体框架模型LINQ查询,这是这样的:Linq2Entities +实体框架查询优化:。凡()与LINQ的地方
from e1 in context.Entity1
from e2 in context.Entity2
from e3summary in
from e3 in context.Entity3
where e3.Field1 = value // <-- this is the line in question
group e3 by new { e3.Field1, e3.Field2, e3.Field3 }
into e3group
select new
{
e3group.Key.Field1,
e3group.Key.Field2,
e3group.Key.Field3,
Total = e3group.Sum(o => o.Field4)
}
where
// conditions on e1 and joining e1, e2, and e3summary
...
select e1;
生成的SQL从选择我的一切e3表(实际上是数据库中的一个视图)作为派生表,然后对派生表应用where子句,对其进行分组,并加入到其他结果中。这几乎正是我想要的,除了我认为我不需要整个e3视图进行分组(它是我的测试数据库中的73M记录,几乎是800M的产品)。我期待在最内层的级别被应用在我的LINQ查询的WHERE子句,而是我得到(我只包括相关部分):
...
INNER JOIN (SELECT
[Extent3].[Field1] AS [K1],
[Extent3].[Field2] AS [K2],
[Extent3].[Field3] AS [K3],
SUM([Extent3].Field4] AS [A1]
FROM (SELECT
[e3].[ID] AS [ID],
[e3].[Field1] AS [Field1],
[e3].[Field2] AS [Field2],
[e3].[Field3] AS [Field3],
[e3].[Field4] AS [Field4],
[e3].[Field5] AS [Field5],
[e3].[Field6] AS [Field6],
[e3].[Field7] AS [Field7],
[e3].[Field8] AS [Field8]
FROM [dbo].[e3] AS [e3]) AS [Extent3]
WHERE ([Extent3].[Field1] = @p__linq__0)
GROUP BY [Extent3].[Field1], [Extent3].[Field2], [Extent3].[Field3]) AS [GroupBy1]
...
我从
改变了我的Linq查询from e3 in context.Entity3
where e3.Field1 = value // <-- this is the line in question
到
from e3 in context.Entity3.Where(e => e.Field1 = value)
,这创造了什么我原先预期,在最内层的级别WHERE子句:
...
FROM [dbo].[e3] AS [e3] WHERE [e3].Field1] = @p__linq__0) AS [Extent3]
GROUP BY [Extent3].[Field1], [Extent3].[Field2], [Extent3].[Field3]) AS [GroupBy1]
为什么在我的上下文中将.Where([condition])
直接应用于集合与在我的Linq查询中有where [condition]
有什么区别?我会认为这将以相同的方式被解析到表达式树中。
P.S.在旁注中,将两个查询放入SQL Server Management Studio并比较查询执行计划,我惊讶地发现执行计划无论如何都是完全相同的。 SQL的查询计划优化器确实令人难以置信!
您关于执行计划相同的最后一点是点对点。由于Field5到Field8根本不在父查询中使用,所以优化器在子查询中完全忽略它们。您可以达到的唯一节约是不会通过线路发送多余的字节查询文本。 – 2011-04-14 18:30:07