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简介
Entity Framework Core (EF Core)是微软推荐的基于.NET Core 的应用程序数据访问技术。开源，轻量级，可扩展并且支持跨平台开发。EF Core是一种对象关系映射器（ORM），通过应用程序实体对象和关系数据库中的数据的映射，使得开发人员能够以面向对象的方式处理数据。
使用
在项目里头安装EF Core和MySQL相关的NuGet包：Microsoft.EntityFrameworkCore，Pomelo.EntityFrameworkCore.MySql ，如果你使用的是其他数据库，那么就换成其他的数据库相关的包即可。
这里创建的是一个web项目，桌面项目其实大同小异，创建一个类继承DbContext，DbContext 是 EF 中非常重要的一个组件，它拥有数据库的会话连接，数据查询，修改保存数据，缓存，事务管理等等作用。
比如我这里创建的是这样的：
代码语言：javascript复制using Acg.Models;
using Microsoft.EntityFrameworkCore;
namespace Acg.DataBase
{
public class AcgbiuDbContext : DbContext
{
public DbSet<TopicModel> Acgbiu_Topic { get; set; }
public DbSet<TopicRelationshipsModel> Acgbiu_Topic_Relationships { get; set; }
public DbSet<TermModel> Acgbiu_Terms { get; set; }
public DbSet<FocusModel> Acgbiu_Focus { get; set; }
public AcgbiuDbContext(DbContextOptions<AcgbiuDbContext> options) : base(options)
{
this.Database.Migrate();
}
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<TopicModel>();
modelBuilder.Entity<TopicRelationshipsModel>();
modelBuilder.Entity<FocusModel>();
}
}
}创建实体类，对应数据库中的表结构，比如我这里的TopicModel。
代码语言：javascript复制using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
namespace Acg.Models
{
[Table("acgbiu_topic")]
public class TopicModel
{
[Key]
public int topic_id { get; set; }
public string name { get; set; }
public string description { get; set; }
public string icon { get; set; }
public string remark { get; set; }
}
}使用依赖注入的方式使用刚才创建的AcgbiuDbContext ，在Startup.cs中注册AcgbiuDbContext。
代码语言：javascript复制public void ConfigureServices(IServiceCollection services)
{
services.AddControllersWithViews();
string connectStr = $"server = 服务器地址; port=端口号;database = 使用的数据库; uid = 数据库连接用户名; password = 密码";
services.AddDbContext<AcgbiuDbContext>(oprions => oprions.UseMySql(connectStr, new MySqlServerVersion(new Version(10,5,6))));
}以一个控制器类的代码为例，看下数据的增删改查。
构造函数注入的方式，获取我们刚才注册的AcgbiuDbContext，然后就可以使用了。
代码语言：javascript复制//获取表的所有数据
AcgbiuDbContext.Acgbiu_Topic.ToList();
//添加数据
AcgbiuDbContext.Acgbiu_Topic.Add(topicModel);
//更新数据
AcgbiuDbContext.Acgbiu_Topic.Update(topicModel);
//删除数据
AcgbiuDbContext.Acgbiu_Topic.Remove(topic);
//异步的方式将前面的增删改，保存到数据库中
await AcgbiuDbContext.SaveChangesAsync();using Acg.DataBase;
using Acg.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
namespace Acg.Controllers
{
[Route("Api/[controller]/[action]/{id?}")]
public class ApiTopicController: ControllerBase
{
private readonly IConfiguration Configuration;
private readonly AcgbiuDbContext AcgbiuDbContext;
public ApiTopicController(IConfiguration configuration, AcgbiuDbContext acgbiuDbContext)
{
Configuration=configuration;
AcgbiuDbContext = acgbiuDbContext;
}
[HttpGet]
public async Task<IActionResult> Topics(int id)
{
List<TopicModel> topicModels = new List<TopicModel>();
topicModels = AcgbiuDbContext.Acgbiu_Topic.ToList();
if (id != 0)
{
TopicModel topicModel = topicModels.Find(x=>x.topic_id==id);
return new JsonResult(topicModel);
}
return new JsonResult(topicModels);
}
[HttpPost]
public async Task<IActionResult> Topics([FromBody] TopicModel topicModel)
{
bool res = true;
AcgbiuDbContext.Acgbiu_Topic.Add(topicModel);
int num=await AcgbiuDbContext.SaveChangesAsync();
if (num <= 0)
{
res = false;
}
return new JsonResult(num);
}
[HttpPut]
public async Task<IActionResult> Topics(int id,[FromBody]TopicModel topicModel)
{
bool res = true;
if (id != topicModel.topic_id)
{
return BadRequest();
}
AcgbiuDbContext.Acgbiu_Topic.Update(topicModel);
int num = await AcgbiuDbContext.SaveChangesAsync();
return new JsonResult(num);
}
[HttpDelete]
public async Task<IActionResult> Topics(long id)
{
var topic = await AcgbiuDbContext.Acgbiu_Topic.FindAsync(id);
if (topic == null)
{
return NotFound();
}
AcgbiuDbContext.Acgbiu_Topic.Remove(topic);
await AcgbiuDbContext.SaveChangesAsync();
return NoContent();
}
[HttpGet]
public async Task<IActionResult> TopicTerms(int id)
{
if (id > 0)
{
var terms = AcgbiuDbContext.Acgbiu_Topic_Relationships.Join(AcgbiuDbContext.Acgbiu_Terms, x => x.term_id, y => y.term_id, (x, y) => new
{
x.id,
x.topic_id,
x.term_id,
y.name,
y.slug
}).Where(p => p.topic_id == id).ToList();
return new JsonResult(terms);
}
else
{
var terms = AcgbiuDbContext.Acgbiu_Topic_Relationships.Join(AcgbiuDbContext.Acgbiu_Terms, x => x.term_id, y => y.term_id, (x, y) => new
{
x.id,
x.topic_id,
x.term_id,
y.name,
y.slug
}).ToList();
return new JsonResult(terms);
}
}
[HttpPost]
public async Task<IActionResult> TopicTerms([FromBody] TopicRelationshipsModel topicRelationshipsModel)
{
try
{
if (topicRelationshipsModel==null||topicRelationshipsModel.topic_id==0|| topicRelationshipsModel.term_id==0)
{
return BadRequest();
}
bool isExist = AcgbiuDbContext.Acgbiu_Topic_Relationships.Any(x=>x.topic_id==topicRelationshipsModel.topic_id&&x.term_id==topicRelationshipsModel.term_id);
if (!isExist)
{
await AcgbiuDbContext.Acgbiu_Topic_Relationships.AddAsync(topicRelationshipsModel);
await AcgbiuDbContext.SaveChangesAsync();
}
else
{
return BadRequest();
}
}catch(Exception ex)
{
return BadRequest();
}
return NoContent();
}
}
}参考
Entity Framework Core 概述 – EF Core | Microsoft Learn
