LINQ to SQL GroupBy，Take和OrderBy

Question

我有一张有记录的桌子

|   ID      |   FKID    |   Date        |   Username        |
--------------------------------------------------------------
|   A       |   a1      |   01/01/01    |       Joe         |
|   B       |   a1      |   02/01/01    |       Joe         |
|   C       |   b1      |   03/01/01    |       Joe         |
|   D       |   b1      |   04/01/01    |       Joe         |
|   E       |   c2      |   05/01/01    |       Joe         |
|   F       |   c2      |   06/01/01    |       Joe         |

我想选择3个具有不同FKID记录， FKID记录的最新日期首先属于Joe 。

|   F       |   c2      |   06/01/01    |       Joe         |
|   D       |   b1      |   04/01/01    |       Joe         |
|   B       |   a1      |   02/01/01    |       Joe         |

我可以达成一项记录：

Table.Where(a => a.Username.Equals("Joe"))
     .GroupBy(a => a.FKID)
     .Select(g => g.FirstOrDefault())
     .ToList<Record>();

但无法使Take()和OrderByDecending()正常工作。

Answer 1

您需要OrderByDescending ：-

Table.Where(a => a.Username.Equals("Joe"))
     .GroupBy(a => a.FKID)
     .Select(g => g.OrderByDescending(x => x.Date).FirstOrDefault())
     .Take(3)
     .ToList<Record>();