Linq -- 集合比较

需求:

    /// 对同一个类型的两个序列(或叫集合,数组) users,users1进行比较,
    /// users1中的元素如果users中没有,就把这些元素与users的元素组合.

解决方案:

 

using System;
using System.Collections.Generic;
using System.Linq;

namespace XMLSpy.Linq{
    /**//// <summary>
    /// 对同一个类型的两个序列(或叫集合,数组) users,users1进行比较,
    /// users1中的元素如果users中没有,就把这些元素与users的元素组合.
    /// Author : xmlspy.spring@gmail.com
    /// </summary>
    public class SetCompare{
        public SetCompare(){
            List<User> users = new List<User>()
                               {
                                   new User(0),
                                   new User(3),
                                   new User(1),
                                   new User(8)
                               };

            List<User> users1 = new List<User>()
                                {
                                    new User(0),
                                    new User(1),
                                    new User(3),
                                    new User(5)
                                };

            Console.WriteLine("------------方式1---------------");
            //方式1:使用扩展方法,必须实现IEqualityComparer<T>接口
            //users1中的元素如果users中没有,就把这些元素与users的元素组合.
            List<User> users2 = users.Union(users1, new UserEqualityComparer()).ToList();

            foreach (User u in users2){
                Console.WriteLine(u.Id);
            }

            /**//////  重新初始化
            users = new List<User>() {
                new User(0),new User(3),
                new User(1),new User(8)
            };

            users1 = new List<User>() {
                new User(0),new User(1),
                new User(3),new User(5)
            };


            Console.WriteLine("------------方式2---------------");
            //方式2:使用Linq语句,不用实现IEqualityComparer<T>接口

            //步骤1:查找出users1中有而users中没有的User序列
            var users3 = from user1 in users1
                         let tem = from user in users select user.Id
                         where tem.Contains(user1.Id) == false
                         select user1;
            //步骤2:添加步骤1的结果到users中
            users.AddRange(users3);

            foreach (User u in users){
                Console.WriteLine(u.Id);
            }
        }
    }

    public class UserEqualityComparer : IEqualityComparer<User>{
        public bool Equals(User x, User y){
            return x.Id == y.Id;
        }

        public int GetHashCode(User obj){
            return obj.Id;
        }
    }

    public class User {
        private int _id;
        private string _name;

        Constructors#region Constructors
        public User(int id) {
            _id = id;
        }
        #endregion

        Properties#region Properties
        public int Id {
            get { return _id; }
            set { _id = value; }
        }
        public string Name {
            get { return _name; }
            set { _name = value; }
        }
        #endregion
    }
}