Linq – 由多个表组成

使用Linq to Sql如何对以下2个表进行分组。

订单表 ：

CustomerID | Name |Date 1 | order1 | 2010-01-01 2 | order2 | 2010-01-01 2 | order3 | 2010-04-01 

电话表 ：

 CustomerID | Name |Date 1 | call1 | 2010-01-01 3 | call2 | 2010-06-01 2 | call3 | 2010-05-01 

我想按日期对两个表进行分组， 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 

我知道如何组合一张桌子，

 from o in Orders group o by o.Date.Date into og select new {Date = og.Key,Orders= og.Count()}; 

我怎么组合两个？ 谢谢！

Answer 1

由于两个表似乎都有类似的结构，我建议将两者都投影到一个等效的forms，然后在这两个集合的串联上进行分组。

 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的惰性，这可能实际上减少为单个查询。 为了表现，我会确保这不是来自地狱的查询。

Answer 2

您可以使用Union方法：

  var result = (from c in Calls group c by c.Date into cg select new {Date = cg.Key, Calls = cg.Count(), Orders = 0}) .Union(from o in Orders group o by o.Date into og select new {Date = og.Key, Calls = 0, Orders = og.Count()}) .GroupBy(x => x.Date) .Select(g => new {Date = g.Key, Calls = g.Max(r => r.Calls), Orders = g.Max(r => r.Orders)}); foreach (var row in result) { Trace.WriteLine(row); } 

这与您要编写的SQL非常相似（两个表的并集，然后是将结果合并为一行的外部查询）