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ASP.NET Core 入门教程 8 ASP.NET Core + Entity Framework Core 数据访问入门

时间：2022-11-20 21:21:34

Core 入门教程 8、 Core + Entity Framework Core 数据访问入门原文: Core 入门教程 8、 Core + Entity Framework Core 数据访问入门

一、前言

1、本教程主要内容

Core MVC 集成 EF Core 介绍&操作步骤 Core MVC 使用 EF Core + Linq to Entity 访问MySQL数据库 Core MVC 使用 EF Core + 原生SQL访问MySql数据库EF Core + MySQL数据库插入数据后获取自增列的值

Entity Framework Core简称为 EF Core

2、本教程环境信息

本篇代码以下代码进行调整：/ken-io/-core-tutorial/tree/master/chapter-02

3、准备工作

安装MySQL数据库：/downloads/mysql/

Windows环境

下载安装包后双击安装，一直下一步即可。

MacOS环境

参考：https://ken.io/note/macos-mysql8-install-config-tutorial

CentOS环境

参考：https://ken.io/note/centos-mysql8-setup

4、前置知识

控制反转（IOC）原则与依赖注入（DI）

Core 默认集成了DI。所有官方模块的引入都要使用DI的方式引入。

/item/IOC

Linq使用教程

/zh-cn/dotnet/csharp/tutorials/working-with-linq

二、EF Core + MySQL 前置准备

EF Core 全称：Entity Framework Core，为微软为 .NET Core平台开发的ORM框架。对应是 .NET Framework平台的Entity Framework（EF），无论是EF还是EF Core都可以说是 .NET 平台开发效率最高的ORM框架。

1、引入 EF Core + MySQL Provider

EF Core已经集成在 Core 中，但默认并不支持MySQL，如果需要连接MySQL,需要添加MySQL相关的Provider，这里我选择的是：Pomelo.EntityFrameworkCore.MySql

任意命令行操作即可，我用的是VS Code自带的命令行

//进入项目根目录： Ken.Tutorial.Webcd Ken.Tutorial.Web//添加Packagedotnet add package Pomelo.EntityFrameworkCore.MySql

这里我添加的 MySql.Data.EntityFrameworkCore 版本是 8.0.13，如果你想跟我使用一样的版本，可以使用以下命令：

dotnet add package Pomelo.EntityFrameworkCore.MySql --version 2.1.4

2、创建MySQL库表

创建数据库

CREATE DATABASE ken_tutorial;

创建表

USE ken_tutorial;DROP TABLE IF EXISTS `user`; CREATE TABLE `user` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(255) DEFAULT NULL, `age` int(11) DEFAULT NULL, `hobby` varchar(500) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

3、配置链接字符串

在项目根目录Ken.Tutorial.Web中创建配置文件appsettings.json,并写入以下配置

{"ConnectionStrings": {"testdb": "server=localhost;database=Ken.Tutorial;uid=root;pwd=root;"}}

4、实体&DbContext准备

创建user表对应实体

在项目根目录Ken.Tutorial.Web中创建目录Models,并在其中创建类：UserEntity.cs

using System;using ponentModel.DataAnnotations;using ponentModel.DataAnnotations.Schema;namespace Ken.Tutorial.Web.Models { [Table("user")] [Serializable] public class UserEntity { [Key]//主键 [DatabaseGenerated(DatabaseGeneratedOption.Identity)]//自增列 [Column("id")] public int Id { get; set; } [Column("name")] public string Name { get; set; } [Column("age")] public int Age { get; set; } [Column("hobby")] public string Hobby { get; set; } } }

创建DBContext

在项目根目录Ken.Tutorial.Web中创建目录Repositories,并在其中创建类：TutorialDbContext.cs

using System;using Microsoft.EntityFrameworkCore;using Microsoft.Extensions.Configuration;namespace Ken.Tutorial.Web.Repositories { public class TutorialDbContext : DbContext { private IConfiguration Configuration { get; } public TutorialDbContext(IConfiguration configuration) { this.Configuration = configuration; } protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) { optionsBuilder.UseMySql(Configuration.GetConnectionString("testdb")); } ppublic DbSet<UserEntity> Users { get; set; } } }

TutorialDbContext 继承了 DbContext，然后再Context初始化时配置MySQL链接。

由于 Core 默认使用了DI组件，所以我们取配置文件，就需要在构造函数中获取IConfiguration注入的实例。

在Startup.cs配置注入，以便数据访问类可以访问DI方式获取TutorialDbContext

public void ConfigureServices(IServiceCollection services) { //引入MVC模块 services.AddMvc(); //配置DbContext注入 services.AddTransient<TutorialDbContext>(); }

三、EF Core + Linq to entity 访问数据库

1、创建Linq To Entity 数据访问类

using System;using System.Collections.Generic;using System.Linq;using Ken.Tutorial.Web.Models;namespace Ken.Tutorial.Web.Repositories { public class TutorialRepository { private TutorialDbContext DbContext { get; } public TutorialRepository(TutorialDbContext dbContext) { //在构造函数中注入DbContext this.DbContext = dbContext; } //添加 public int Add(UserEntity user) { using (DbContext) { //由于我们在UserEntity.Id配置了自增列的Attribute，EF执行完成后会自动把自增列的值赋值给user.Id DbContext.Users.Add(user); return DbContext.SaveChanges(); } } //删除 public int Delete(int id) { using (DbContext) { var userFromContext = DbContext.Users.FirstOrDefault(u => u.Id == id); DbContext.Users.Remove(userFromContext); return DbContext.SaveChanges(); } } //更新 public int Update(UserEntity user) { using (DbContext) { var userFromContext = DbContext.Users.FirstOrDefault(u => u.Id == user.Id); userFromContext.Name = user.Name; userFromContext.Age = user.Age; userFromContext.Hobby = user.Hobby; return DbContext.SaveChanges(); } } //查询 public UserEntity QueryById(int id) { using (DbContext) { return DbContext.Users.FirstOrDefault(u => u.Id == id); } } //查询集合 public List<UserEntity> QueryByAge(int age) { using (DbContext) { return DbContext.Users.Where(u => u.Age == age).ToList(); } } //查看指定列 public List<string> QueryNameByAge(int age) { using (DbContext) { return DbContext.Users.Where(u => u.Age == age).Select(u => u.Name).ToList(); } } //分页查询 public List<UserEntity> QueryUserPaging(int pageSize, int page) { using (DbContext) { return DbContext.Users.Skip(pageSize * (page - 1)).Take(pageSize).ToList(); } } //事务：将年龄<0的用户修改年龄为0 public int FixAge() { using (DbContext) { using (var transaction = DbContext.Database.BeginTransaction()) { try { var userListFromContext = DbContext.Users.Where(u => u.Age < 0); foreach (UserEntity u in userListFromContext) { u.Age = 0; } var count = DbContext.SaveChanges(); mit(); return count; } catch { transaction.Rollback(); return 0; } } } } } }

2、创建测试API

在Controllers文件夹下创建EfCoreController.cs作为访问入口

using System;using Ken.Tutorial.Web.Models;using Ken.Tutorial.Web.Repositories;using Microsoft.AspNetCore.Mvc;namespace Ken.Tutorial.Web.Controllers { public class EfCoreController : Controller { public TutorialRepository Repository { get; } public EfCoreController(TutorialRepository repository) { this.Repository = repository; } public IActionResult Add(UserEntity user) { var message = Repository.Add(user) > 0 ? "success" : "failed"; return Json(new { Message = message, User = user }); } public IActionResult Delete(int id) { var message = Repository.Delete(id) > 0 ? "success" : "failed"; return Json(new { Message = message }); } public IActionResult Update(UserEntity user) { var message = Repository.Update(user) > 0 ? "success" : "failed"; return Json(new { Message = message, User = user }); } public IActionResult QueryById(int id) { var user = Repository.QueryById(id); return Json(new { User = user }); } public IActionResult QueryByAge(int age) { var users = Repository.QueryByAge(age); return Json(new { Users = users }); } public IActionResult QueryNameByAge(int age) { var users = Repository.QueryNameByAge(age); return Json(new { Users = users }); } public IActionResult QueryUserPaging(int pageSize, int page) { var users = Repository.QueryUserPaging(pageSize, page); return Json(new { Users = users }); } public IActionResult FixAge() { var count = Repository.FixAge(); return Json(new { FixCount = count }); } } }

3、启动测试

在Startup.cs中配置Repository注入

public void ConfigureServices(IServiceCollection services) { //其他代码省略 //配置Repository注入 services.AddTransient<TutorialRepository>(); }

启动项目并测试

四、EF Core + 原生SQL 访问数据库

1、创建EF Core + 原生SQL 数据访问类

using System;using System.Collections.Generic;using System.Data;using System.Data.SqlClient;using System.Linq;using Ken.Tutorial.Web.Models;using Microsoft.EntityFrameworkCore;using MySql.Data.MySqlClient;namespace Ken.Tutorial.Web.Repositories{public class TutorialWithSqlRepository{private TutorialDbContext DbContext { get; }public TutorialWithSqlRepository(TutorialDbContext dbContext){//在构造函数中注入DbContextthis.DbContext = dbContext;}//添加public int Add(UserEntity user){using (var connection = DbContext.Database.GetDbConnection()){connection.Open();var command = connection.CreateCommand() as MySqlCommand;mandText = "INSERT INTO user (name,age,hobby) VALUES(@name,@age,@hobby)";command.Parameters.Add(new MySqlParameter(){ParameterName = "@name",DbType = DbType.String,Value = user.Name});command.Parameters.Add(new MySqlParameter(){ParameterName = "@age",DbType = DbType.Int32,Value = user.Age});command.Parameters.Add(new MySqlParameter(){ParameterName = "@hobby",DbType = DbType.String,Value = user.Hobby});var count = command.ExecuteNonQuery();//获取插入时产生的自增列Id并赋值给user.Id使用user.Id = (int)command.LastInsertedId;return count;}}//删除public int Delete(int id){using (DbContext){return DbContext.Database.ExecuteSqlCommand("DELETE FROM user WHERE id={0}", id);}}//更新public int Update(UserEntity user){using (DbContext){return DbContext.Database.ExecuteSqlCommand("UPDATE user SET name={0}, age={1}, hobby={2} WHERE id={3}",user.Name, user.Age, user.Hobby, user.Id);}}//查询public UserEntity QueryById(int id){using (DbContext){return DbContext.Users.FromSql("SELECT id,name,age,hobby FROM user WHERE id={0}", id).FirstOrDefault();}}//查询集合public List<UserEntity> QueryByAge(int age){using (DbContext){return DbContext.Users.FromSql("SELECT id,name,age,hobby FROM user WHERE age={0}", age).ToList();}}//查看指定列public List<string> QueryNameByAge(int age){using (DbContext){return DbContext.Users.FromSql("SELECT id,name FROM user WHERE age={0}", age).Select(u => u.Name).ToList();}}//分页查询public List<UserEntity> QueryUserPaging(int pageSize, int page){using (DbContext){return DbContext.Users.FromSql("SELECT id,name,age,hobby FROM user LIMIT {0},{1}", pageSize * (page - 1), pageSize).ToList();}}//事务：将年龄<0的用户修改年龄为0public int FixAge(){using (DbContext){using (var connection = DbContext.Database.GetDbConnection()){//打开连接connection.Open();//开启事务using (var transaction = connection.BeginTransaction()){try{//获取命令对象var command = connection.CreateCommand();command.Transaction = transaction;mandText = "UPDATE user SET age=@age WHERE age<@age";command.Parameters.Add(new MySqlParameter(){ParameterName = "@age",DbType = DbType.Int32,Value = 0});var count = command.ExecuteNonQuery();mit();return count;}catch (Exception ex){connection.Close();transaction.Rollback();return 0;}}}}}}}

2、创建测试API

在Controllers文件夹下创建EfCoreWithSqlController.cs作为访问入口

using System;using Ken.Tutorial.Web.Models;using Ken.Tutorial.Web.Repositories;using Microsoft.AspNetCore.Mvc;namespace Ken.Tutorial.Web.Controllers { public class EfCoreWithSqlController : Controller { public TutorialWithSqlRepository Repository { get; } public EfCoreWithSqlController(TutorialWithSqlRepository repository) { this.Repository = repository; } public IActionResult Add(UserEntity user) { var message = Repository.Add(user) > 0 ? "success" : "failed"; return Json(new { Message = message, User = user }); } public IActionResult Delete(int id) { var message = Repository.Delete(id) > 0 ? "success" : "failed"; return Json(new { Message = message }); } public IActionResult Update(UserEntity user) { var message = Repository.Update(user) > 0 ? "success" : "failed"; return Json(new { Message = message, User = user }); } public IActionResult QueryById(int id) { var user = Repository.QueryById(id); return Json(new { User = user }); } public IActionResult QueryByAge(int age) { var users = Repository.QueryByAge(age); return Json(new { Users = users }); } public IActionResult QueryNameByAge(int age) { var users = Repository.QueryNameByAge(age); return Json(new { Users = users }); } public IActionResult QueryUserPaging(int pageSize, int page) { var users = Repository.QueryUserPaging(pageSize, page); return Json(new { Users = users }); } public IActionResult FixAge() { var count = Repository.FixAge(); return Json(new { FixCount = count }); } } }