1、Join操作符
Join操作符类似于SQL语句中的Join语句用于连接多个表，Linq to OBJECT中Join操作符可以用来连接两个输入序列。
例如，
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ConsoleApplication{ class Program { static void Main(string[] args) { List pList = new List(); People p1 = new People(1, "C", 4); People p2 = new People(2, "Java", 7); People p3 = new People(3, "Python", 11); People p4 = new People(4, "Linux", 15); People p5 = new People(5,"CJavaPY",1); pList.Add(p1); pList.Add(p2); pList.Add(p3); pList.Add(p4); pList.Add(p5); List rList = new List(); Record r1 = new Record(1, 3); Record r2 = new Record(2, 5); Record r3 = new Record(3, 7); Record r4 = new Record(4, 20); Record r5 = new Record(5, 11); rList.Add(r1); rList.Add(r2); rList.Add(r3); rList.Add(r4); rList.Add(r5); var Items = pList.Join(rList, p => p.Id, r => r.PId, (p, r) => new { Name = p.Name, WarRecord = r.WarRecord }); foreach (var item in Items) { Console.WriteLine(item.Name + ":" + item.WarRecord); } Console.ReadKey(); } } public class People { public People(int id, string name, int age) { this.Id = id; this.Name = name; this.Age = age; } public int Id { get; set; } public string Name { get; set; } public int Age { get; set; } } public class Record { public Record(int id, int warRecord) { this.PId = id; this.WarRecord = warRecord; } public int PId { get; set; } public int WarRecord { get; set; } }} 2、GroupJoin操作符
GroupJoin操作符也用于连接两个输入序列，但与Join操作符不同稍有不同，Join操作符在列举outer序列元素时，会将一个outer序列元素和其对应的inner序列元素作为一组参数传递给委托resultSelector委托，也就是如果某一个outer序列元素有多个对应的inner序列元素，Join操作符将会分多次将outer序列元素和每一个对应的inner序列元素传递给委托resultSelector。使用GroupJoin操作符时，如果某一个outer序列元素有多个对应的inner序列元素，那么这多个对应的inner序列元素会作用一个序列一次性传递给委托resultSelecotr，可以针对此序列添加一些处理逻辑。
例如，
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ConsoleApplication{ class Program { static void Main(string[] args) { List pList = new List(); People p1 = new People(1, "C", 4); People p2 = new People(2, "Java", 7); People p3 = new People(3, "Python", 11); People p4 = new People(4, "Linux", 15); People p5 = new People(5,"CJavaPY",1); pList.Add(p1); pList.Add(p2); pList.Add(p3); pList.Add(p4); pList.Add(p5); List rList = new List(); Record r1 = new Record(1, 3); Record r2 = new Record(2, 5); Record r3 = new Record(3, 7); Record r4 = new Record(4, 20); Record r5 = new Record(1, 11); rList.Add(r1); rList.Add(r2); rList.Add(r3); rList.Add(r4); rList.Add(r5); var Items = pList.Join(rList, p => p.Id, r => r.PId, (p, r) => new { Name = p.Name, WarRecord = r.WarRecord }); foreach (var item in Items) { Console.WriteLine(item.Name + ":" + item.WarRecord); } Console.WriteLine(); var Items1 = pList.GroupJoin(rList, p => p.Id, r => r.PId, (p, List1) => new { Name = p.Name, WarRecords = List1.Sum(r=>r.WarRecord) }); //Join与GrouyJoin的不同，Join每次都会传递一个元素到输出序列，而GruopJoin会将相同序列序号作为一个集合的形式传递给输出委托 foreach (var item in Items1) { Console.WriteLine(item.Name + ":" + item.WarRecords); } } } public class People { public People(int id, string name, int age) { this.Id = id; this.Name = name; this.Age = age; } public int Id { get; set; } public string Name { get; set; } public int Age { get; set; } } public class Record { public Record(int id, int warRecord) { this.PId = id; this.WarRecord = warRecord; } public int PId { get; set; } public int WarRecord { get; set; } }}