C#基础：LINQ之Join查询

Join查询可以用一个查询，搜索两个相关数据，用键字段把结果连接起来

示例代码如下：

1.  class Customer
2.     {
3.         public string ID { get; set; }
4.         public string City { get; set; }
5.         public string Country { get; set; }
6.         public string Region { get; set; }
7.         public decimal Sales { get; set; }
8.     }
9.     class Order
10.     {
11.         public string ID { get; set; }
12.         public decimal Amount { get; set; }
13.     }
14.     class Program
15.     {
16.         static void Main(string[] args)
17.         {
18.             List<Order> orders = new List<Order> {
19.               new Order { ID="P", Amount=100 },
20.               new Order { ID="Q", Amount=200 },
21.               new Order { ID="R", Amount=300 },
22.               new Order { ID="S", Amount=400 },
23.               new Order { ID="T", Amount=500 },
24.               new Order { ID="U", Amount=600 },
25.               new Order { ID="V", Amount=700 },
26.               new Order { ID="W", Amount=800 },
27.               new Order { ID="X", Amount=900 },
28.               new Order { ID="Y", Amount=1000 },
29.               new Order { ID="Z", Amount=1100 }
30.             };
31.             List<Customer> customers = new List<Customer> {
32.               new Customer { ID="A", City="New York", Country="USA", Region="North America", Sales=9999},
33.               new Customer { ID="B", City="Mumbai", Country="India", Region="Asia", Sales=8888},
34.               new Customer { ID="C", City="Karachi", Country="Pakistan", Region="Asia", Sales=7777},
35.               new Customer { ID="D", City="Delhi", Country="India", Region="Asia", Sales=6666},
36.               new Customer { ID="E", City="São Paulo", Country="Brazil", Region="South America", Sales=5555 },
37.               new Customer { ID="F", City="Moscow", Country="Russia", Region="Europe", Sales=4444 },
38.               new Customer { ID="G", City="Seoul", Country="Korea", Region="Asia", Sales=3333 },
39.               new Customer { ID="H", City="Istanbul", Country="Turkey", Region="Asia", Sales=2222 },
40.               new Customer { ID="I", City="Shanghai", Country="China", Region="Asia", Sales=1111 },
41.               new Customer { ID="J", City="Lagos", Country="Nigeria", Region="Africa", Sales=1000 },
42.               new Customer { ID="K", City="Mexico City", Country="Mexico", Region="North America", Sales=2000 },
43.               new Customer { ID="L", City="Jakarta", Country="Indonesia", Region="Asia", Sales=3000 },
44.               new Customer { ID="M", City="Tokyo", Country="Japan", Region="Asia", Sales=4000 },
45.               new Customer { ID="N", City="Los Angeles", Country="USA", Region="North America", Sales=5000 },
46.               new Customer { ID="O", City="Cairo", Country="Egypt", Region="Africa", Sales=6000 },
47.               new Customer { ID="P", City="Tehran", Country="Iran", Region="Asia", Sales=7000 },
48.               new Customer { ID="Q", City="London", Country="UK", Region="Europe", Sales=8000 },
49.               new Customer { ID="R", City="Beijing", Country="China", Region="Asia", Sales=9000 },
50.               new Customer { ID="S", City="Bogotá", Country="Colombia", Region="South America", Sales=1001 },
51.               new Customer { ID="T", City="Lima", Country="Peru", Region="South America", Sales=2002 }
52.            };
53.             //Join查询
54.             var queryResults =
55.                from c in customers
56.                join o in orders on c.ID equals o.ID            //用join连接两个查询数据
57.                select new { c.ID, c.City, SalesBefore = c.Sales, NewOrder = o.Amount, SalesAfter = c.Sales + o.Amount };
58.             foreach (var item in queryResults)
59.             {
60.                 WriteLine(item);
61.             }        
62.         }
63.     }