如何使用LINQ选择最新的和不同的记录? [英] How can I select the most recent and distinct records using LINQ?

问题描述

我正在尝试使用LINQ从状态历史记录中获取记录的最新状态.我在下订单时遇到麻烦，或者我完全不合时宜.

I'm trying to get the latest status of a recorded from a history of statuses using LINQ. I'm having trouble with my order or maybe I'm completely off the mark.

我的代码

Dim LatestStatusTable= (From RecordHistoryTable In db.RecordHistory) _
    .GroupBy(Function(i) i.Status).[Select](Function(i) i.First())

示例数据

Data

ID    Timestamp                 Status
251   2017-07-19 11:01:15.577   2
250   2017-07-14 16:15:38.543   2
249   2017-07-13 13:31:13.010   2
249   2017-07-14 04:16:08.307   1
249   2017-07-14 05:45:38.437   2
249   2017-07-14 08:00:42.253   1
249   2017-07-14 08:30:02.380   2
248   2017-07-11 15:30:28.223   2
248   2017-07-11 18:31:11.857   1
248   2017-07-11 18:49:08.510   2

Desired Output

ID    Timestamp                 Status
251   2017-07-19 11:01:15.577   2
250   2017-07-14 16:15:38.543   2
249   2017-07-14 08:30:02.380   2
248   2017-07-11 18:49:08.510   2

有人可以教育我并指出正确的方向吗?

Can someone please educate me and point me in the right direction?

推荐答案

GroupBy ID然后选择时，要在Timestamp上选择OrderByDescending，然后在每个组中使用First.

GroupBy ID then when selecting, you want to OrderByDescending on Timestamp, then take the First in each group.

Dim LatestStatusTable = (From RecordHistoryTable In db.RecordHistory) _
    .GroupBy(Function(i) i.ID) _
    .[Select](Function(g) g.OrderByDescending(Function(x) x.Timestamp).First())

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