ASP.NET Core 入门教程 8、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(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 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
{
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 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 - 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();
transaction.Commit();
return count;
}
catch
{
transaction.Rollback();
return 0;
}
}
}
}
}
}

2、创建测试API

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
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 - 1), 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 = 0
});
var count = command.ExecuteNonQuery();
transaction.Commit();
return count;
}
catch (Exception ex)
{
connection.Close();
transaction.Rollback();
return 0;
}
} }
}
}
}
}

2、创建测试API

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 });
} }
}

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

五、备注

1、附录

  • 本文代码示例

https://github.com/ken-io/asp.net-core-tutorial/tree/master/chapter-08

  • 本文参考

https://docs.microsoft.com/zh-cn/ef/core
https://www.learnentityframeworkcore.com
https://mysql-net.github.io/MySqlConnector/tutorials/net-core-mvc/



本文首发于我的独立博客:https://ken.io/note/asp.net-core-tutorial-entity-framework-core-mysql

上一篇:SQL Server数据库————模糊查询和聚合函数


下一篇:062、如何使用flannel host-gw backend(2019-04-02 周二)