EF. How to union tables, sort rows, and get top entities?

问题:

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?

回答1:

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); 

回答2:

How about something like:

var top10 = EFentity.t2.Union(EFentity.t1.ToList()).OrderBy(t=>t.Timestamp).ToList().Take(10); 

文章来源: EF. How to union tables, sort rows, and get top entities?