LINQ的 - 组由多个表 [英] Linq - Group by multiple tables
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问题描述
使用LINQ到SQL我如何组的以下2个表。
Using Linq to Sql how do i group the following 2 tables.
订单表
CustomerID | Name |Date
1 | order1 | 2010-01-01
2 | order2 | 2010-01-01
2 | order3 | 2010-04-01
调用表
CustomerID | Name |Date
1 | call1 | 2010-01-01
3 | call2 | 2010-06-01
2 | call3 | 2010-05-01
我要组两个表按日期,结果
Date | Orders | Calls
2010-01-01 | 2 | 1
2010-04-01 | 1 | 0
2010-05-01 | 0 | 1
2010-06-01 | 0 | 1
我知道如何组一个表,
i know how to group a single table ,
from o in Orders
group o by o.Date.Date into og
select new {Date = og.Key,Orders= og.Count()};
如何组中的两个?
THX!
推荐答案
由于两个表似乎有一个类似的结构,我建议那些两套串联两个突出成等价的形式,然后组。
Since both tables seem to have a similar structure I'd recommend projecting both into an equivalent form and then group on the concatenation of those two sets.
var orders = from o in Orders
select new { IsOrder = true, o.Date };
var calls = from c in Calls
select new { IsOrder = false, c.Date };
var result = from x in orders.Concat(calls)
group x by x.Date into og
select new {Date = og.Key, Orders= og.Count(o=>o.IsOrder), Calls = og.Count(c=>!c.IsTrue)};
由于LINQ2SQL的懒惰天性这实际上可能减少到一个单一的查询。在性能的利益我会确保这是不是来自地狱的查询。
Due to the lazy nature of Linq2Sql this might actually be reduced to a single query. In the interest of performance I would make sure this is not a query from hell.
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