LINQ中Cancat操作符(九)

LINQ中的连接操作符主要包括Join()和GroupJoin()两个.

一、Join()操作符

 Join()操作符非常类似于T-SQL中的inner join，它将两个数据源进行连接，根据两个数据源中相等的值进行匹配

Sample Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConnectOperation
{
    public class Category
    {
        public int Id { get; set; }
        public string CategoryName { get; set; }
        public DateTime CreateTime { get; set; }
    }

    public class Product
    {
        public int Id { get; set; }
        public int CategoryId { get; set; }
        public string Name { get; set; }
        public double Price { get; set; }
        public DateTime CreateTime { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            // 初始化数据
            List<Category> listCategory = new List<Category>()
            {
              new Category(){ Id=1,CategoryName="计算机",CreateTime=DateTime.Now.AddYears(-1)},
              new Category(){ Id=2,CategoryName="文学",CreateTime=DateTime.Now.AddYears(-2)},
              new Category(){ Id=3,CategoryName="高校教材",CreateTime=DateTime.Now.AddMonths(-34)},
              new Category(){ Id=4,CategoryName="心理学",CreateTime=DateTime.Now.AddMonths(-34)}
            };
            List<Product> listProduct = new List<Product>()
            {
               new Product(){Id=1,CategoryId=1, Name="C#高级编程第10版", Price=100.67,CreateTime=DateTime.Now},
               new Product(){Id=2,CategoryId=1, Name="Redis开发和运维", Price=69.9,CreateTime=DateTime.Now.AddDays(-19)},
               new Product(){Id=3,CategoryId=2, Name="活着", Price=57,CreateTime=DateTime.Now.AddMonths(-3)},
               new Product(){Id=4,CategoryId=3, Name="高等数学", Price=97,CreateTime=DateTime.Now.AddMonths(-1)},
               new Product(){Id=5,CategoryId=6, Name="国家宝藏", Price=52.8,CreateTime=DateTime.Now.AddMonths(-1)}
            };

            // 1、查询表达式
            var queryExpress = from c in listCategory
                               join p in listProduct on c.Id equals p.CategoryId
                               select new { Id = c.Id, CategoryName = c.CategoryName, ProductName = p.Name, PublishTime = p.CreateTime };
            Console.WriteLine("查询表达式输出:");
            foreach (var item in queryExpress)
            {
                Console.WriteLine($"id:{item.Id},CategoryName:{item.CategoryName},ProductName:{item.ProductName},PublishTime:{item.PublishTime}");
            }

            Console.WriteLine("方法语法输出:");
            // 2、方法语法
            var queryFun = listCategory.Join(listProduct, c => c.Id, p => p.CategoryId, (c, p) => new { Id = c.Id, CategoryName = c.CategoryName, ProductName = p.Name, PublishTime = p.CreateTime });
            foreach (var item in queryFun)
            {
                Console.WriteLine($"id:{item.Id},CategoryName:{item.CategoryName},ProductName:{item.ProductName},PublishTime:{item.PublishTime}");
            }

            Console.ReadKey();
        }
    }
}

View Code