LINQ基于最新日期的条目总数 [英] LINQ Sum of entries based on latest date

问题描述

我有一张像这样的桌子:

I have a table like so:

Code | BuildDate  | BuildQuantity
---------------------------------
1    | 2013-04-10 | 4
1    | 2014-09-23 | 1
1    | 2014-08-20 | 2
7    | 2014-02-05 | 4

我希望LINQ查询为每个代码选择最新的构建日期，为该代码选择BuildQuantity，以此类推，对所有记录进行汇总.因此，对于上述数据，结果应为 1 + 4 = 5 .

I want the LINQ query to pick up the LATEST Build date for each Code, pick the BuildQuantity for that Code, and so on for all the records, and sum it up. So for the data above, the result should be 1 + 4 = 5.

这就是我要尝试的:

var built = (from tb in db.Builds
             orderby tb.BuildDate descending
             group tb by tb.Code into tbgrp
             select tbgrp.Sum(c => c.BuildQuantity)).First();

此查询返回7 ...我在做什么错了?

This query returns 7... What am I doing wrong?

推荐答案

在获取第一个代码之前，您要对所有代码的BuildQuantities求和，而不是要对第一个代码求和.

You are summing all code's BuildQuantities before you take the first, instead you want to sum the firsts.

int built = db.Builds
    .GroupBy(b => b.Code)
    .Sum(g => g.OrderByDescending(b => b.BuildDate).First().BuildQuantity); 

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