C#9引入的自定义类型record

Posted 2021-04-14 dotNET跨平台

record是C#9引入的新的引用类型，详细见官方文档：https://docs.microsoft.com/zh-cn/dotnet/csharp/whats-new/csharp-9#record-types

DDD中，有实体和值对象的概念，其中值对象定义如下：

通过对象属性值来识别的对象，它将多个相关属性组合为一个概念整体——《实现领域驱动设计》

就是通过这个对象的各个属性相同不相同来判断是不是同一个值对象，这时，record就最合适不过了，它能直接判断两个实例化后的对象是否相等，。

record本质上个class，对反射，dapper的适配，面向对象的特征都是相同的，demo见：https://github.com/axzxs2001/Asp.NetCoreExperiment/blob/master/Asp.NetCoreExperiment/CSharp/RecordTypeDemo/Program.cs

using Dapper;using Npgsql;using System;using System.Collections.Generic;using System.Linq;using System.Reflection;
namespace RecordTypeDemo{

 class Program { static void Main(string[] args) { //接口类型 IShow show = new Entity1() { ID = 1, Name = "桂素伟" }; Console.WriteLine(show); //输出结果：Entity1 { ID = 1, Name = 桂素伟 } //抽象类型 Entity entity = new Entity1() { ID = 1, Name = "桂素伟" }; Console.WriteLine(entity); //输出结果：Entity1 { ID = 1, Name = 桂素伟 } //注1:虽然 类型名{属性名1=属性值,属性名2=属性值,……} 相等，但比较结果是不等的 Console.WriteLine($"show == entity结果：{show == entity}"); //输出结果：show == entity结果：：False //实体类型 var entity1 = new Entity1() { ID = 1, Name = "桂素伟" }; Console.WriteLine(entity1); //输出结果：Entity1 { ID = 1, Name = 桂素伟 } Console.WriteLine($"(entity1 == entity结果：{entity1 == entity}"); //输出结果：(entity1 == entity结果：True Console.WriteLine($"(entity1 == entity结果：{entity1.Equals(entity)}"); //输出结果：(entity1 == entity结果：True AddEntity(entity);
 ReflectionTest(entity1); }
 /// <summary> /// 反射中使用record，和类相山 /// </summary> /// <param name="entity"></param> static void ReflectionTest(Entity entity) { var type = Assembly.GetExecutingAssembly().GetType("RecordTypeDemo.Entity"); Console.WriteLine(type.IsClass); } /// <summary> /// 对dapper适配 /// </summary> /// <param name="entity"></param> /// <returns></returns> static bool AddEntity(Entity entity) { using (var con = new NpgsqlConnection("Server=127.0.0.1;Port=5432;UserId=postgres;Password=postgres2018;Database=postgres;")) { var list = con.Query<Entity1>("select * from entitys").ToList(); if (!list.Contains(entity)) { con.Execute("insert into entitys(id,name) values(@id,@name)", entity); } return true; } /*表结构CREATE TABLE public.entitys( id integer NOT NULL DEFAULT nextval('entitys_id_seq'::regclass), name character varying(256) COLLATE pg_catalog."default", CONSTRAINT entitys_pkey PRIMARY KEY (id))*/ } }
 #region 面向对象特征和类一样 /// <summary> /// 接口 /// </summary> public interface IShow { void Show(); } /// <summary> /// 抽象记录 /// </summary> public abstract record Entity : IShow { public abstract int ID { get; set; }
 public abstract string Name { get; set; }
 public void Show() { Console.WriteLine($"{this.GetType().Name}:"); Console.WriteLine($"{this.ToString()}"); } } /// <summary> /// 记录 /// </summary> public record Entity1 : Entity { public override int ID { get; set; } public override string Name { get; set; } } #endregion}