LINQ到实体：容易找到SQL最大值，但很难在LINQ？ [英] Linq-to-entities: Easy to find max value in SQL, but difficult in LINQ?

问题描述

我已经开始使用LINQ到实体.NET 3.5，和我遇到一个情况下，我可以做在SQL中真正的轻松，但我有很大的困难LINQ。 我有一个表中有三个字段一个SQL数据库，出于这个例子中，我会打电话给他们富，酒吧，和foo_index和填充他们像这样：

I've started using Linq-to-entities with .NET 3.5, and I've come across a scenario that I can do real easy in SQL, but I'm having great difficulty with linq. I have a table in a SQL database with three fields, for purposes of this example I'll call them foo, bar, and foo_index and populate them like so:

块引用

FOO |酒吧| foo_index

foo | bar | foo_index

555 101 1

555 101 1

555 101 2

555 101 2

555 101 3

555 101 3

555 101 4

555 101 4

555 101 5

555 101 5

要得到的是什么吧最大foo_index其中foo = 555 SQL是

To get what bar is at the max foo_index where foo=555 the SQL is

SELECT bar, max(foo_index) as max_foo_index
FROM T
WHERE foo=555
GROUP BY bar

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我已经写了一些LINQ到实体code在C＃中的作品，但我有一种感觉，有一种更高贵的解决方案在那里，而且我错过了一些概念，将进行以下容易得多。此外，有没有什么办法其他然后一个foreach获取数据了变种的？

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I've written some linq-to-entities code in C# that works, but I have a feeling there is a much more elegent solution out there, and that I'm missing some concept that would make the following much easier. Also, is there any way other then a foreach to get the data out of a var?

db_entity db = new db_entity();

var q =
     from table in db.T
     where table.FOO == 555
     select new { table.BAR, table.FOO_INDEX };

var q2 = 
     from t2 in q
     where t2.FOO_INDEX == table.Max(r => r.FOO_INDEX)
     select new { t2.BAR };

int result = 0;

foreach (var record in q2}
{
    result = record.BAR.Value;
}

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任何帮助或指导，将AP preciated，谢谢！

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Any help or guidance would be appreciated, Thanks!

推荐答案

我觉得这应该工作：

var query = from item in db.T
            where item.FOO == 555
            group item by item.BAR into g
            select new { Bar = g.Key, Max = g.Max(x => x.FOO_INDEX) };

所以基本上你正在做同样的方法，因为在SQL：组数据，然后采取组内的键组和最大FOO_INDEX

So basically you're taking the same approach as in the SQL: group the data, then take the key for the group and the maximum FOO_INDEX within the group.

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