上一篇文章(https://www.cnblogs.com/meowv/p/12909558.html)完善了项目中的代码，接入了Swagger。本篇主要使用Entity Framework Core完成对数据库的访问，以及使用Code-First的方式进行数据迁移，自动创建表结构。
在.EntityFrameworkCore项目中添加我们的数据访问上下文对象MeowvBlogDbContext，继承自 AbpDbContext<T>。然后重写OnModelCreating方法。
OnModelCreating：定义EF Core 实体映射。先调用 base.OnModelCreating 让 abp 框架为我们实现基础映射，然后调用builder.Configure()扩展方法来配置应用程序的实体。当然也可以不用扩展，直接写在里面，这样一大坨显得不好看而已。
在abp框架中，可以使用 [ConnectionStringName] Attribute 为我们的DbContext配置连接字符串名称。先加上，然后再在appsettings.json中进行配置，因为之前集成了多个数据库，所以这里我们也配置多个连接字符串，与之对应。
本项目默认采用MySql，你可以选择任意你喜欢的。
//MeowvBlogDbContext.csusing Microsoft.EntityFrameworkCore;using Volo.Abp.Data;using Volo.Abp.EntityFrameworkCore;namespace Meowv.Blog.EntityFrameworkCore{ [ConnectionStringName("MySql")] public class MeowvBlogDbContext : AbpDbContext<MeowvBlogDbContext> { public MeowvBlogDbContext(DbContextOptions<MeowvBlogDbContext> options) : base(options) { } protected override void OnModelCreating(ModelBuilder modelBuilder) { base.OnModelCreating(modelBuilder); modelBuilder.Configure(); } }}//appsettings.json{ "ConnectionStrings": { "Enable": "MySQL", "MySql": "Server=localhost;User Id=root;Password=123456;Database=meowv_blog_tutorial", "SqlServer": "", "PostgreSql": "", "Sqlite": "" }}然后新建我们的扩展类MeowvBlogDbContextModelCreatingExtensions.cs和扩展方法Configure()。注意，扩展方法是静态的，需加static
//MeowvBlogDbContextModelCreatingExtensions.csusing Microsoft.EntityFrameworkCore;using Volo.Abp;namespace Meowv.Blog.EntityFrameworkCore{ public static class MeowvBlogDbContextModelCreatingExtensions { public static void Configure(this ModelBuilder builder) { Check.NotNull(builder, nameof(builder)); ... } }}完成上述操作后在我们的模块类MeowvBlogFrameworkCoreModule中将DbContext注册到依赖注入，根据你配置的值使用不同的数据库。在.Domain层创建配置文件访问类AppSettings.cs
//AppSettings.csusing Microsoft.Extensions.Configuration;using System.IO;namespace Meowv.Blog.Domain.Configurations{ /// <summary> /// appsettings.json配置文件数据读取类 /// </summary> public class AppSettings { /// <summary> /// 配置文件的根节点 /// </summary> private static readonly IConfigurationRoot _config; /// <summary> /// Constructor /// </summary> static AppSettings() { // 加载appsettings.json，并构建IConfigurationRoot var builder = new ConfigurationBuilder().SetBasePath(Directory.GetCurrentDirectory()) .AddJsonFile("appsettings.json", true, true); _config = builder.Build(); } /// <summary> /// EnableDb /// </summary> public static string EnableDb => _config["ConnectionStrings:Enable"]; /// <summary> /// ConnectionStrings /// </summary> public static string ConnectionStrings => _config.GetConnectionString(EnableDb); }}获取配置文件内容比较容易，代码中有注释也很容易理解。
值得一提的是，ABP会自动为DbContext中的实体创建默认仓储. 需要在注册的时使用options添加AddDefaultRepositories()。
默认情况下为每个实体创建一个仓储，如果想要为其他实体也创建仓储，可以将 includeAllEntities 设置为 true，然后就可以在服务中注入和使用 IRepository<TEntity> 或 IQueryableRepository<TEntity>
//MeowvBlogFrameworkCoreModule.csusing Meowv.Blog.Domain;using Meowv.Blog.Domain.Configurations;using Microsoft.Extensions.DependencyInjection;using Volo.Abp.EntityFrameworkCore;using Volo.Abp.EntityFrameworkCore.MySQL;using Volo.Abp.EntityFrameworkCore.PostgreSql;using Volo.Abp.EntityFrameworkCore.Sqlite;using Volo.Abp.EntityFrameworkCore.SqlServer;using Volo.Abp.Modularity;namespace Meowv.Blog.EntityFrameworkCore{ [DependsOn( typeof(MeowvBlogDomainModule), typeof(AbpEntityFrameworkCoreModule), typeof(AbpEntityFrameworkCoreMySQLModule), typeof(AbpEntityFrameworkCoreSqlServerModule), typeof(AbpEntityFrameworkCorePostgreSqlModule), typeof(AbpEntityFrameworkCoreSqliteModule) )] public class MeowvBlogFrameworkCoreModule : AbpModule { public override void ConfigureServices(ServiceConfigurationContext context) { context.Services.AddAbpDbContext<MeowvBlogDbContext>(options => { options.AddDefaultRepositories(includeAllEntities: true); }); Configure<AbpDbContextOptions>(options => { switch (AppSettings.EnableDb) { case "MySQL": options.UseMySQL(); break; case "SqlServer": options.UseSqlServer(); break; case "PostgreSql": options.UsePostgreSql(); break; case "Sqlite": options.UseSqlite(); break; default: options.UseMySQL(); break; } }); } }}现在可以来初步设计博客所需表为：发表文章表(posts)、分类表(categories)、标签表(tags)、文章对应标签表(post_tags)、友情链接表(friendlinks)
在.Domain层编写实体类，Post.cs、Category.cs、Tag.cs、PostTag.cs、FriendLink.cs。把主键设置为int型，直接继承Entity
//Post.csusing System;using Volo.Abp.Domain.Entities;namespace Meowv.Blog.Domain.Blog{ /// <summary> /// Post /// </summary> public class Post : Entity<int> { /// <summary> /// 标题 /// </summary> public string Title { get; set; } /// <summary> /// 作者 /// </summary> public string Author { get; set; } /// <summary> /// 链接 /// </summary> public string Url { get; set; } /// <summary> /// HTML /// </summary> public string Html { get; set; } /// <summary> /// Markdown /// </summary> public string Markdown { get; set; } /// <summary> /// 分类Id /// </summary> public int CategoryId { get; set; } /// <summary> /// 创建时间 /// </summary> public DateTime CreationTime { get; set; } }}//Category.csusing Volo.Abp.Domain.Entities;namespace Meowv.Blog.Domain.Blog{ /// <summary> /// Category /// </summary> public class Category : Entity<int> { /// <summary> /// 分类名称 /// </summary> public string CategoryName { get; set; } /// <summary> /// 展示名称 /// </summary> public string DisplayName { get; set; } }}//Tag.csusing Volo.Abp.Domain.Entities;namespace Meowv.Blog.Domain.Blog{ /// <summary> /// Tag /// </summary> public class Tag : Entity<int> { /// <summary> /// 标签名称 /// </summary> public string TagName { get; set; } /// <summary> /// 展示名称 /// </summary> public string DisplayName { get; set; } }}//PostTag.csusing Volo.Abp.Domain.Entities;namespace Meowv.Blog.Domain.Blog{ /// <summary> /// PostTag /// </summary> public class PostTag : Entity<int> { /// <summary> /// 文章Id /// </summary> public int PostId { get; set; } /// <summary> /// 标签Id /// </summary> public int TagId { get; set; } }}//FriendLink.csusing Volo.Abp.Domain.Entities;namespace Meowv.Blog.Domain.Blog{ /// <summary> /// FriendLink /// </summary> public class FriendLink : Entity<int> { /// <summary> /// 标题 /// </summary> public string Title { get; set; } /// <summary> /// 链接 /// </summary> public string LinkUrl { get; set; } }}创建好实体类后，在MeowvBlogDbContext添加DbSet属性
//MeowvBlogDbContext.cs... [ConnectionStringName("MySql")] public class MeowvBlogDbContext : AbpDbContext<MeowvBlogDbContext> { public DbSet<Post> Posts { get; set; } public DbSet<Category> Categories { get; set; } public DbSet<Tag> Tags { get; set; } public DbSet<PostTag> PostTags { get; set; } public DbSet<FriendLink> FriendLinks { get; set; } ... }...在.Domain.Shared层添加全局常量类MeowvBlogConsts.cs和表名常量类MeowvBlogDbConsts.cs，搞一个表前缀的常量，我这里写的是meowv_，大家可以随意。代表我们的表名都将以meowv_开头。然后在MeowvBlogDbConsts中将表名称定义好。
//MeowvBlogConsts.csnamespace Meowv.Blog.Domain.Shared{ /// <summary> /// 全局常量 /// </summary> public class MeowvBlogConsts { /// <summary> /// 数据库表前缀 /// </summary> public const string DbTablePrefix = "meowv_"; }}//MeowvBlogDbConsts.csnamespace Meowv.Blog.Domain.Shared{ public class MeowvBlogDbConsts { public static class DbTableName { public const string Posts = "Posts"; public const string Categories = "Categories"; public const string Tags = "Tags"; public const string PostTags = "Post_Tags"; public const string Friendlinks = "Friendlinks"; } }}在Configure()方法中配置表模型，包括表名、字段类型和长度等信息。对于下面代码不是很明白的可以看看微软的自定义 Code First 约定：https://docs.microsoft.com/zh-cn/ef/ef6/modeling/code-first/conventions/custom
//MeowvBlogDbContextModelCreatingExtensions.csusing Meowv.Blog.Domain.Blog;using Meowv.Blog.Domain.Shared;using Microsoft.EntityFrameworkCore;using Volo.Abp;using static Meowv.Blog.Domain.Shared.MeowvBlogDbConsts;namespace Meowv.Blog.EntityFrameworkCore{ public static class MeowvBlogDbContextModelCreatingExtensions { public static void Configure(this ModelBuilder builder) { Check.NotNull(builder, nameof(builder)); builder.Entity<Post>(b => { b.ToTable(MeowvBlogConsts.DbTablePrefix + DbTableName.Posts); b.HasKey(x => x.Id); b.Property(x => x.Title).HasMaxLength(200).IsRequired(); b.Property(x => x.Author).HasMaxLength(10); b.Property(x => x.Url).HasMaxLength(100).IsRequired(); b.Property(x => x.Html).HasColumnType("longtext").IsRequired(); b.Property(x => x.Markdown).HasColumnType("longtext").IsRequired(); b.Property(x => x.CategoryId).HasColumnType("int"); b.Property(x => x.CreationTime).HasColumnType("datetime"); }); builder.Entity<Category>(b => { b.ToTable(MeowvBlogConsts.DbTablePrefix + DbTableName.Categories); b.HasKey(x => x.Id); b.Property(x => x.CategoryName).HasMaxLength(50).IsRequired(); b.Property(x => x.DisplayName).HasMaxLength(50).IsRequired(); }); builder.Entity<Tag>(b => { b.ToTable(MeowvBlogConsts.DbTablePrefix + DbTableName.Tags); b.HasKey(x => x.Id); b.Property(x => x.TagName).HasMaxLength(50).IsRequired(); b.Property(x => x.DisplayName).HasMaxLength(50).IsRequired(); }); builder.Entity<PostTag>(b => { b.ToTable(MeowvBlogConsts.DbTablePrefix + DbTableName.PostTags); b.HasKey(x => x.Id); b.Property(x => x.PostId).HasColumnType("int").IsRequired(); b.Property(x => x.TagId).HasColumnType("int").IsRequired(); }); builder.Entity<FriendLink>(b => { b.ToTable(MeowvBlogConsts.DbTablePrefix + DbTableName.Friendlinks); b.HasKey(x => x.Id); b.Property(x => x.Title).HasMaxLength(20).IsRequired(); b.Property(x => x.LinkUrl).HasMaxLength(100).IsRequired(); }); } }}此时项目层级目录如下
在.EntityFrameworkCore.DbMigrations中新建模块类MeowvBlogEntityFrameworkCoreDbMigrationsModule.cs、数据迁移上下文访问对象MeowvBlogMigrationsDbContext.cs和一个Design Time Db Factory类MeowvBlogMigrationsDbContextFactory.cs
模块类依赖MeowvBlogFrameworkCoreModule模块和AbpModule。并在ConfigureServices方法中添加上下文的依赖注入。
//MeowvBlogEntityFrameworkCoreDbMigrationsModule.csusing Microsoft.Extensions.DependencyInjection;using Volo.Abp.Modularity;namespace Meowv.Blog.EntityFrameworkCore.DbMigrations.EntityFrameworkCore{ [DependsOn( typeof(MeowvBlogFrameworkCoreModule) )] public class MeowvBlogEntityFrameworkCoreDbMigrationsModule : AbpModule { public override void ConfigureServices(ServiceConfigurationContext context) { context.Services.AddAbpDbContext<MeowvBlogMigrationsDbContext>(); } }}MeowvBlogMigrationsDbContext和MeowvBlogDbContext没什么大的区别
//MeowvBlogMigrationsDbContext.csusing Microsoft.EntityFrameworkCore;using Volo.Abp.EntityFrameworkCore;namespace Meowv.Blog.EntityFrameworkCore.DbMigrations.EntityFrameworkCore{ public class MeowvBlogMigrationsDbContext : AbpDbContext<MeowvBlogMigrationsDbContext> { public MeowvBlogMigrationsDbContext(DbContextOptions<MeowvBlogMigrationsDbContext> options) : base(options) { } protected override void OnModelCreating(ModelBuilder builder) { base.OnModelCreating(builder); builder.Configure(); } }}MeowvBlogMigrationsDbContextFactory类主要是用来使用Code-First命令的(Add-Migration 和 Update-Database ...)
需要注意的地方，我们在这里要单独设置配置文件的连接字符串，将.HttpApi.Hosting层的appsettings.json复制一份到.EntityFrameworkCore.DbMigrations，你用了什么数据库就配置什么数据库的连接字符串。
//appsettings.json{ "ConnectionStrings": { "Default": "Server=localhost;User Id=root;Password=123456;Database=meowv_blog" }}//MeowvBlogMigrationsDbContextFactory.csusing Microsoft.EntityFrameworkCore;using Microsoft.EntityFrameworkCore.Design;using Microsoft.Extensions.Configuration;using System.IO;namespace Meowv.Blog.EntityFrameworkCore.DbMigrations.EntityFrameworkCore{ public class MeowvBlogMigrationsDbContextFactory : IDesignTimeDbContextFactory<MeowvBlogMigrationsDbContext> { public MeowvBlogMigrationsDbContext CreateDbContext(string[] args) { var configuration = BuildConfiguration(); var builder = new DbContextOptionsBuilder<MeowvBlogMigrationsDbContext>() .UseMySql(configuration.GetConnectionString("Default")); return new MeowvBlogMigrationsDbContext(builder.Options); } private static IConfigurationRoot BuildConfiguration() { var builder = new ConfigurationBuilder() .SetBasePath(Directory.GetCurrentDirectory()) .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true); return builder.Build(); } }}到这里差不多就结束了，默认数据库meowv_blog_tutorial是不存在的，先去创建一个空的数据库。
然后在Visual Studio中打开程序包管理控制台，将.EntityFrameworkCore.DbMigrations设为启动项目。
键入命令：Add-Migration Initial,会发现报错啦，错误信息如下：
Add-Migration : 无法将“Add-Migration”项识别为 cmdlet、函数、脚本文件或可运行程序的名称。请检查名称的拼写，如果包括路径，请确保路径正确，然后再试一次。所在位置 行:1 字符: 1+ Add-Migration Initial+ ~~~~~~~~~~~~~ + CategoryInfo : ObjectNotFound: (Add-Migration:String) [], CommandNotFoundException + FullyQualifiedErrorId : CommandNotFoundException 这是因为我们少添加了一个包，要使用代码优先方式迁移数据，必须添加，Microsoft.EntityFrameworkCore.Tools。
紧接着直接用命令安装Install-Package Microsoft.EntityFrameworkCore.Tools包，再试一遍
可以看到已经成功，并且生成了一个Migrations文件夹和对应的数据迁移文件
最后输入更新命令：Update-Database，然后打开数据瞅瞅。
完美，成功创建了数据库表，而且命名也是我们想要的，字段类型也是ok的。__efmigrationshistory表是用来记录迁移历史的，这个可以不用管。当我们后续如果想要修改添加表字段，新增表的时候，都可以使用这种方式来完成。
解决方案层级目录图，供参考
本篇使用Entity Framework Core完成数据访问和代码优先的方式创建数据库表，你学会了吗？
联系客服
