使用EF Core的Code First模式,通过迁移来同步数据库与模型.

环境: JetBrains Rider Window10 .NET5

一. 创建项目

1. 使用JetBrains Rider创建一个web api项目

2. 使用NuGet安装依赖包

   • Microsoft.EntityFrameworkCore
   • Microsoft.EntityFrameworkCore.Tools
   • Microsoft.EntityFrameworkCore.SqlServer 此依赖包根据使用的数据库安装相应的包, 这里使用的是SQL Server

3. 创建数据库上下文

   • 在项目中建立一个Data文件夹，创建一个类TestDBContext

     using Microsoft.EntityFrameworkCore;
     
     namespace Test.Data
     {
         public class TestDBContext : DbContext
         {
             public TestDBContext(DbContextOptions<TestDBContext> options) : base(options){}
         }
     }
     

4. 创建数据模型

   • 在项目中建立一个Models文件夹，创建部门类Department, 员工类Personnel

     using System.Collections.Generic;
     using System.ComponentModel.DataAnnotations;
     using System.ComponentModel.DataAnnotations.Schema;
     
     namespace Test.Models
     {
         /// <summary>
         /// 部门类
         /// </summary>
         public class Department
         {
             [Key] // 主键
             [DatabaseGenerated(DatabaseGeneratedOption.Identity)]  //设置自增
             public int Id { get; set; }
             
             [Required]
             [MaxLength(50)]
             public string Name { get; set; }
     
             // Department 与 Personnel 一对多
             public ICollection<Personnel> Personnels { get; set; } = new List<Personnel>();
         }
     }
     

     using System.ComponentModel.DataAnnotations;
     using System.ComponentModel.DataAnnotations.Schema;
     
     namespace Test.Models
     {
         /// <summary>
         /// 员工类
         /// </summary>
         public class Personnel
         {
             [Key]
             [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
             public int Id { get; set; }
             
             [Required]
             [MaxLength(50)]
             public string Name { get; set; }
             
             public int Age { get; set; }
             
             [ForeignKey("Department")] // 外键
             public int DepartmentId { get; set; }
         }
     }
     

5. 在之前创建的数据库上下文TestDBContext中注册数据模型

   using Microsoft.EntityFrameworkCore;
   using Test.Models;
   
   namespace Test.Data
   {
       public class TestDBContext : DbContext
       {
           public TestDBContext(DbContextOptions<TestDBContext> options) : base(options){}
           
           // 注册数据模型
           // 模型集的名称与对应的表名相同
           public DbSet<Department> Departments { get; set; }
           public DbSet<Personnel> Personnels { get; set; }
       }
   }
   

6. 在appsettings.json中添加数据库连接字符串

   {
     "Logging": {
       "LogLevel": {
         "Default": "Information",
         "Microsoft": "Warning",
         "Microsoft.Hosting.Lifetime": "Information"
       }
     },
     "AllowedHosts": "*",
     "connectionStrings": {
       "SqlServerContext": "Data Source=服务器名;Initial Catalog=数据库名; User Id=用户名;Password=密码"
     }
   }
   

7. 在Startup中注册数据库上下文TestDBContext

   using Microsoft.AspNetCore.Builder;
   using Microsoft.AspNetCore.Hosting;
   using Microsoft.EntityFrameworkCore;
   using Microsoft.Extensions.Configuration;
   using Microsoft.Extensions.DependencyInjection;
   using Microsoft.Extensions.Hosting;
   using Microsoft.OpenApi.Models;
   using Test.Data;
   
   namespace Test
   {
       public class Startup
       {
           // 注入 IConfiguration:有关配置文件最底层的一个接口类型
           public Startup(IConfiguration configuration)
           {
               _Configuration = configuration;
           }
   
           private IConfiguration _Configuration { get; }
   
           // This method gets called by the runtime. Use this method to add services to the container.
           public void ConfigureServices(IServiceCollection services)
           {
               services.AddControllers();
               services.AddSwaggerGen(c => { c.SwaggerDoc("v1", 
                   new OpenApiInfo {Title = "Test", Version = "v1"}); });
               // 注册数据库上下文
               // _Configuration["connectionStrings:SqlServerContext"] 获取数据库连接字符串
               services.AddDbContext<TestDBContext>(option
                   => option.UseSqlServer(_Configuration["connectionStrings:SqlServerContext"]));
           }
   
           // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
           public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
           {
               if (env.IsDevelopment())
               {
                   app.UseDeveloperExceptionPage();
                   app.UseSwagger();
                   app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "Test v1"));
               }
   
               app.UseHttpsRedirection();
   
               app.UseRouting();
   
               app.UseAuthorization();
   
               app.UseEndpoints(endpoints => { endpoints.MapControllers(); });
           }
       }
   }
   

8. 迁移

   • 打开Terminal窗口或者cmd进入项目根目录执行迁移命令: dotnet ef migrations add 本次迁移的名称
   • 如果未安装dotnet ef, 会无法执行
   • 安装全局dotnet ef
   • 再次执行迁移命令
   • 迁移成功后, 项目中有一个Migrations目录, 保存着每次迁移的记录

9. 更新数据库

   • 执行dotnet ef database update
   • 数据库更新成功, 数据库就已经创建好了
   • 当数据模型发生改变时, 只用再次执行迁移/更新数据库

二. 添加初始数据

1. 在数据上下文TestDBContext中重写OnModelCreating方法

   using System.Collections.Generic;
   using Microsoft.EntityFrameworkCore;
   using Test.Models;
   
   namespace Test.Data
   {
       public class TestDBContext : DbContext
       {
           public TestDBContext(DbContextOptions<TestDBContext> options) : base(options){}
           
           // 注册数据模型
           // 模型集的名称与对应的表名相同
           public DbSet<Department> Departments { get; set; }
           public DbSet<Personnel> Personnels { get; set; }
   
           // 控制数据库和模型映射, 通过它可以自定义映射关系
           protected override void OnModelCreating(ModelBuilder modelBuilder)
           {
               modelBuilder.Entity<Department>()
                   .HasData(new List<Department>()
                   {
                       new Department() {Id = 1, Name = "人力资源部"},
                       new Department() {Id = 2, Name = "技术部"}
                   });
               modelBuilder.Entity<Personnel>()
                   .HasData(new List<Personnel>()
                   {
                       new Personnel() {Id = 1, Name = "张三", Age = 23, DepartmentId = 2},
                       new Personnel() {Id = 2, Name = "李四", Age = 20, DepartmentId = 1},
                       new Personnel() {Id = 3, Name = "王五", Age = 25, DepartmentId = 2}
                   });
               base.OnModelCreating(modelBuilder);
           }
       }
   }
   

2. 迁移, 更新数据库

   

ASP.NET Core通过EF Core连接数据库

原文：https://www.cnblogs.com/z212021/p/14880966.html