Question

使用EF 4.1计算表格中项目的最佳效果是什么？

this.context.MyTable.Count(x.idTenant == 5);

或

 this.context.MyTable.Where(x.idTenant == 5).Count();

计算表中实体的任何其他方法，是否更高效？

Answer 1

在LINQPad中尝试这样做表明生成的sql是相同的：

var r1 = Users.Count(u => u.JurisdictionId == 5).Dump();    
var r2 = Users.Where(u => u.JurisdictionId == 5).Count().Dump();

和生成的sql：

SELECT 
[GroupBy1].[A1] AS [C1]
FROM ( SELECT 
    COUNT(1) AS [A1]
    FROM [System].[Users] AS [Extent1]
    WHERE 5 = [Extent1].[JurisdictionId]
)  AS [GroupBy1]
GO

SELECT 
[GroupBy1].[A1] AS [C1]
FROM ( SELECT 
    COUNT(1) AS [A1]
    FROM [System].[Users] AS [Extent1]
    WHERE 5 = [Extent1].[JurisdictionId]
)  AS [GroupBy1]

这是使用EF 4.2，但这在4.1中应该是相同的。

Answer 2

根据Linq的输出，表达式在它们生成的SQL中是相同的：

SELECT COUNT(*) AS [value]
FROM [MyTable] AS [t0]
WHERE [t0].[idTenant] = @p0

EF 4 Count（）选项性能

2 个答案: