EF。如何联合表格，排序行和获取顶级实体？ [英] EF. How to union tables, sort rows, and get top entities?

问题描述

我想从2个表中的联合记录，对它们进行排序，并从结果集中读取TOP行。

  T1 
 -------- 
 Id，Timestamp，Text1 
 
 T2 
 -------- 
 Id，时间戳，Text2 
  

使用SQL可以这样做：

  SELECT TOP 10 * FROM 
（
 SELECT 
 [Timestamp]，
 [Text1] 
 
 FROM 
 T1 
 
 UNION 
 
 SELECT 
 [Timestamp]，
 [Text2] 
 
 FROM 
 T2 
）as x 
 
 ORDER BY [Timestamp] 
  

问：如何使用EF linq执行该任务？

解决方案

您需要具有相同属性名称和类型的匿名类型，才能执行 Union 操作：

  var t1List = from all in all $ $ $ $ $ $ $ $ $ $ $ b TimeStamp = a.TimeStamp，
 Text = a.Text1 
}; 
 var t2List = from b in allT2 
选择新
 {
 TimeStamp = b.TimeStamp，
 Text = b.Text2 
}; 
 
 var result = t1List.Union（t2List）.OrderBy（ab => ab.TimeStamp）.Take（10）; 
  

I want to union records from 2 tables, sort them, and read TOP rows from result set.

T1
--------
Id, Timestamp, Text1

T2
--------
Id, Timestamp, Text2

With SQL it can be done this way:

SELECT TOP 10 * FROM
(
    SELECT 
        [Timestamp], 
        [Text1] 

    FROM 
        T1

    UNION

    SELECT 
        [Timestamp], 
        [Text2]

    FROM 
        T2
) as x

ORDER BY [Timestamp]

Q: How can I do that task using EF linq?

解决方案

You need an anonymous type with the same property names and types before you can do an Union operation:

var t1List = from a in allT1
        select new
        {
            TimeStamp = a.TimeStamp,
            Text = a.Text1
        };
var t2List = from b in allT2
        select new
        {
            TimeStamp = b.TimeStamp,
            Text = b.Text2
        };

var result = t1List.Union(t2List).OrderBy(ab => ab.TimeStamp).Take(10);

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