linq to sql 连接分组 使用join和into

先附上源代码再说明吧：

 

源代码如下：

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Collections;namespace consoleTest2{ class Transport { public string Name { get; set; } public string How { get; set; } public Transport(string n, string h) { Name = n; How = h; } } class vehicle { public string vehicleName { get; set; } public string vehicleHow { get; set; } public vehicle(string n, string h) { vehicleName = n; vehicleHow = h; } } class Program { static void Main(string[] args) { vehicle[] vehicles = { new vehicle("a","Land"), new vehicle("b","Air"), new vehicle("c","Sea"), new vehicle("d","Air"), new vehicle("e","Sea"), new vehicle("f","Land"), new vehicle("g","Sea"), new vehicle("g","Sea"), new vehicle("g","Sea"), new vehicle("g","Sea"), }; // An array of transports. Transport[] transports = { new Transport("Bicycle", "Land"), new Transport("Balloon", "Air"), new Transport("Boat", "Sea"), new Transport("Jet", "Air"), new Transport("Canoe", "Sea"), new Transport("Biplane", "Air"), new Transport("Car", "Land"), new Transport("Cargo Ship", "Sea"), new Transport("Train", "Land") }; // Create a query that uses a group join to produce // a list of item names and IDs organized by category. var byHow = from how in vehicles join trans in transports on how.vehicleHow equals trans.How into lst select new { How=how, Tlist = lst };////总共创建了10个对象。根据上面的对象数组（vehicle）来进行的。 // Execute the query and display the results. int count = 0; foreach (var t in byHow) { Console.WriteLine("the type of transports{0}", t.How.vehicleName); count++; foreach(var r in t.Tlist) { Console.WriteLine(r.How+" "+r.Name); } } Console.WriteLine(count); } } } 

 

 

 var byHow = from how in  vehicles

                        join trans in transports

                        on how.vehicleHow equals trans.How

                        into lst                                           //    此lst是IEnumerable<transport> 类型

                        select new { How=how, Tlist = lst };

   注意：在select以前的代码，lst 代表的是经过筛选后匹配的实例，一般是一个枚举类型，这时两数据源并没有合并在一起，

           还只是分开。若要选择具体显示的字段时，可以在select执行new操作。确定刷选的字符。

 

 

此句的运行原理为：1：从vehicles取出每一个对象，再将每一个对象how与transports中how进行匹配，此时一个vehicles可能匹配多个transports对象，也就是一对多的关系。如果vehicles有10个对象，那么将进行10次的匹配，不管vehicles中对象的字段是否有相同的值。都会进行一一的匹配。