在查询中按行字段递减排序 [英] Order by descending by row field in query

问题描述

我想写一个EF查询，它根据条件按升序或降序进行排序。以下是我的伪代码：

I want to write a EF query which does order by ascending or descending based on condition. Following is the my pseudo code:

      var result= q.OrderByDescending(x => x.StatusId == 3)
                         if( x.StatusId == 3) 
                              then order by x.ReserveDate
                         if( x.StatusId != 3 ) 
                              then order by descending x.LastUpdateDate

我该怎么做？

更新

这与 q =条件不同q.OrderBy（..）：q.OrderByDescending（..）在引用的重复问题中标记，排序顺序根据行内的值而不是查询外部的标志而不同。

This is not same as q = condition ? q.OrderBy(..) : q.OrderByDescending(..) as marked in referenced duplicate question, sorting order differs based on value within the row instead of a flag outside query.

推荐答案

您可以在OrderBy中提供复杂的表达式...

You can supply complex expressions in OrderBy...

// you might have to give bounding start,end for
// for this query to work correctly...

var end = DateTime.Now;
var start = end.AddYears(-100);

var result = q.OrderBy( 
               x => x.StatusId == 3 ?  

               // this will sort by in ascending order 
               DbFunctions.DiffDays(x.ReserveDate, start) :

               // this will sort in descending order
               DbFunctions.DiffDays(end, x.LastUpdateDate) );

SQL生成将

SELECT 
    ...
    ...
    FROM ( SELECT CASE 
        WHEN ([Extent2].[StatusId ] = 3) 
            THEN DATEDIFF (day, @p__linq__0, [Extent1].[ReserveDate]) 
        ELSE 
            DATEDIFF (day, [Extent1].[LastUpdateDate], @p__linq__1) 
        END AS [C1] 
        FROM  [dbo].[Table] AS [Extent1]
    )  AS [Project1]
    ORDER BY [Project1].[C1]

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