ASP.NET Core 入门笔记9，ASP.NET Core + Entity Framework Core 数据访问入门

一、前言

1、本教程主要内容

ASP.NET Core MVC 集成 EF Core 介绍&操作步骤
ASP.NET Core MVC 使用 EF Core + Linq to Entity 访问MySQL数据库
ASP.NET 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

软件/环境	说明
操作系统	Windows 10
SDK	2.1.401
ASP.NET Core	2.1.3
MySQL	8.0.x
IDE	Visual Studio Code 1.30
浏览器	Chrome 70

VS Code插件	版本	说明
C#	1.17.1	提供C#智能感知， .NET Core 调试、编译等
vscdoe-solution-explorer	0.3.1	提供解决方案视图

本篇代码以下代码进行调整：https://github.com/ken-io/asp.net-core-tutorial/tree/master/chapter-02

3、准备工作

安装MySQL数据库：https://dev.mysql.com/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）

ASP.NET 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。

https://baike.baidu.com/item/IOC

Linq使用教程

https://docs.microsoft.com/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 ASP.NET 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.Web

cd Ken.Tutorial.Web

//添加Package

dotnet 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() NOT NULL AUTO_INCREMENT,

  `name` varchar() DEFAULT NULL,

  `age` int() DEFAULT NULL,

  `hobby` varchar() 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 System.ComponentModel.DataAnnotations;

using System.ComponentModel.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

{

    //宏观上我们可以认为这个类就是数据库本身

    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"));//需要添加引用：MySQL.Data.EntityFrameworkCore

        }

        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 ASP.NET 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 - )).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 < );

                        foreach (UserEntity u in userListFromContext)

                        {

                            u.Age = ;

                        }

                        var count = DbContext.SaveChanges();

                        transaction.Commit();

                        return count;

                    }

                    catch

                    {

                        transaction.Rollback();

                        return ;

                    }

                }

            }

        }

    }

}

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) >  ? "success" : "failed";

            return Json(new { Message = message, User = user });

        }

        public IActionResult Delete(int id)

        {

            var message = Repository.Delete(id) >  ? "success" : "failed";

            return Json(new { Message = message });

        }

        public IActionResult Update(UserEntity user)

        {

            var message = Repository.Update(user) >  ? "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

API	示例
添加用户	/efcore/add?name=ken&age=18&hobby=coding
删除用户	/efcore/delete?id=0
更新用户	/efcore/update?id=1&name=ken&age=666&hobby=codingOrGaming
查询单个用户	/efcore/querybyid?id=0
查询多个用户	/efcore/querybyage?age=18
查询多个用户名	/efcore/querynamebyage?age=18
分页查询用户	/efcore/queryuserpaging?pagesize=3&page=1
修复异常年龄	/efcore/fixage

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DbContext

            this.DbContext = dbContext;

        }

        //添加

        public int Add(UserEntity user)

        {

            using (var connection = DbContext.Database.GetDbConnection())

            {

                connection.Open();

                var command = connection.CreateCommand() as MySqlCommand;

                command.CommandText = "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 - ), pageSize).ToList();

            }

        }

        //事务：将年龄<0的用户修改年龄为0

        public 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;

                            command.CommandText = "UPDATE user SET age=@age WHERE age<@age";

                            command.Parameters.Add(new MySqlParameter()

                            {

                                ParameterName = "@age",

                                DbType = DbType.Int32,

                                Value =

                            });

                            var count = command.ExecuteNonQuery();

                            transaction.Commit();

                            return count;

                        }

                        catch (Exception ex)

                        {

                            connection.Close();

                            transaction.Rollback();

                            return ;

                        }

                    }

                }

            }

        }

    }

}

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) >  ? "success" : "failed";

            return Json(new { Message = message, User = user });

        }

        public IActionResult Delete(int id)

        {

            var message = Repository.Delete(id) >  ? "success" : "failed";

            return Json(new { Message = message });

        }

        public IActionResult Update(UserEntity user)

        {

            var message = Repository.Update(user) >  ? "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<TutorialWithSqlRepository>();

}

启动项目并测试

API	示例
添加用户	/efcorewithsql/add?name=ken&age=18&hobby=coding
删除用户	/efcorewithsql/delete?id=0
更新用户	/efcorewithsql/update?id=1&name=ken&age=666&hobby=codingOrGaming
查询单个用户	/efcorewithsql/querybyid?id=0
查询多个用户	/efcorewithsql/querybyage?age=18
查询多个用户名	/efcorewithsql/querynamebyage?age=18
分页查询用户	/efcorewithsql/queryuserpaging?pagesize=3&page=1
修复异常年龄	/efcorewithsql/fixage

本文摘抄自：https://www.cnblogs.com/ken-io/p/aspnet-core-tutorial-entity-framework-core-mysql.html

如有侵权，请告知删除或者修改