在linq查询上优化dateTime

Question

嗨,大家好,我正面临性能问题.
当我在查询中声明的dateTime运行此查询时

var temp = (from p in db.BEM_EVT_FULL
                      where (p.date_reception > new DateTime(2015,01,01))
                      group p by p.mc_object into g
                      orderby g.Count() descending
                      select new StringIntType
                      {
                          str = g.Key,
                          nbr = g.Count()}).Take(50).ToList();

在sql server profiler中,它被转换为该查询

SELECT TOP (50) 
[Project1].[C3] AS [C1], 
[Project1].[mc_object] AS [mc_object], 
[Project1].[C2] AS [C2]
FROM ( SELECT 
    [GroupBy1].[A1] AS [C1], 
    [GroupBy1].[A2] AS [C2], 
    [GroupBy1].[K1] AS [mc_object], 
    1 AS [C3]
    FROM ( SELECT 
        [Extent1].[mc_object] AS [K1], 
        COUNT(1) AS [A1], 
        COUNT(1) AS [A2]
        FROM [dbo].[BEM_EVT_FULL] AS [Extent1]
        WHERE [Extent1].[date_reception] > convert(datetime2, '2015-01-01 00:00:00.0000000', 121)
        GROUP BY [Extent1].[mc_object]
    )  AS [GroupBy1]
)  AS [Project1]
ORDER BY [Project1].[C1] DESC

并且它工作得很好它在1s以下执行

现在当我在查询之外声明DateTime并运行此查询时

DateTime dt = new DateTime(2015,01,01);

        var temp = (from p in db.BEM_EVT_FULL
                      where (p.date_reception > dt)
                      group p by p.mc_object into g
                      orderby g.Count() descending
                      select new StringIntType
                      {
                          str = g.Key,
                          nbr = g.Count()
                      }).Take(50).ToList();

在sql server profiler中,它被转换为该查询

exec sp_executesql N'SELECT TOP (50) 
[Project1].[C3] AS [C1], 
[Project1].[mc_object] AS [mc_object], 
[Project1].[C2] AS [C2]
FROM ( SELECT 
    [GroupBy1].[A1] AS [C1], 
    [GroupBy1].[A2] AS [C2], 
    [GroupBy1].[K1] AS [mc_object], 
    1 AS [C3]
    FROM ( SELECT 
        [Extent1].[mc_object] AS [K1], 
        COUNT(1) AS [A1], 
        COUNT(1) AS [A2]
        FROM [dbo].[BEM_EVT_FULL] AS [Extent1]
        WHERE [Extent1].[date_reception] > @p__linq__0
        GROUP BY [Extent1].[mc_object]
    )  AS [GroupBy1]
)  AS [Project1]
ORDER BY [Project1].[C1] DESC',N'@p__linq__0 datetime2(7)',@p__linq__0='2015-01-01 00:00:00'

由于DateTime声明,我需要知道应该做什么更改来声明DateTime outisde查询,并获得与第一个查询相同的性能,因此需要大约5百万才能得到exectued,所有这些差异.

Answer 1

其原因（我认为）是在第一种情况下，DateTime 是一个编译时间常量，但在第二种情况下它不是，因此 EF 必须将其作为参数传递。