Question

在尝试解决问题时，我注意到如果我执行LINQ to Entities查询：

var timeRecords = db.Timesheets
.Where(timesheet => timesheet.TimesheetHeaderID == headerID);

我得到这样的查询：

SELECT 
[Extent1].[ID] AS [ID], 
[Extent1].[TimesheetHeaderID] AS [TimesheetHeaderID], 
[Extent1].[StartDateTime] AS [StartDateTime], 
[Extent1].[EndDateTime] AS [EndDateTime], 
[Extent1].[ProjectCode] AS [ProjectCode], 
[Extent1].[TaskCode] AS [TaskCode], 
[Extent1].[WorkDescription] AS [WorkDescription]
FROM [dbo].[Timesheet] AS [Extent1]
WHERE [Extent1].[TimesheetHeaderID] = @p__linq__0

但如果我像这样添加OrderByDescending()：

var timeRecords = db.Timesheets
.Where(timesheet => timesheet.TimesheetHeaderID == headerID)
.OrderByDescending(timesheet => timesheet.StartDateTime);

我得到一个包含如下子查询的查询：

SELECT 
[Project1].[ID] AS [ID], 
[Project1].[TimesheetHeaderID] AS [TimesheetHeaderID], 
[Project1].[StartDateTime] AS [StartDateTime], 
[Project1].[EndDateTime] AS [EndDateTime], 
[Project1].[ProjectCode] AS [ProjectCode], 
[Project1].[TaskCode] AS [TaskCode], 
[Project1].[WorkDescription] AS [WorkDescription]
FROM ( SELECT 
    [Extent1].[ID] AS [ID], 
    [Extent1].[TimesheetHeaderID] AS [TimesheetHeaderID], 
    [Extent1].[StartDateTime] AS [StartDateTime], 
    [Extent1].[EndDateTime] AS [EndDateTime], 
    [Extent1].[ProjectCode] AS [ProjectCode], 
    [Extent1].[TaskCode] AS [TaskCode], 
    [Extent1].[WorkDescription] AS [WorkDescription]
    FROM [dbo].[Timesheet] AS [Extent1]
    WHERE [Extent1].[TimesheetHeaderID] = @p__linq__0
)  AS [Project1]
ORDER BY [Project1].[StartDateTime] DESC

子查询有什么意义？

Answer 1

我猜这个子查询适用于＆＃34; Where＆＃34; part（Where（timesheet =＆gt; timesheet.TimesheetHeaderID == headerID），主查询用于OrderByDescending部分（OrderByDescending（timesheet =＆gt; timesheet.StartDateTime））。所以我假设LINQ的内部机制是分别处理每个链命令。

为什么添加OrderByDescending在LINQ to Entities中添加子查询？

1 个答案: