基于 abp vNext 和 .NET Core 开发博客项目

上一篇文章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。

数据访问

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.cs
using 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.cs
using 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.cs
using 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IConfigurationRootvar 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.cs
using 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。关于这点可以参考ABP文档，https://docs.abp.io/zh-Hans/abp/latest/Entities

//Post.cs
using 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.cs
using 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.cs
using 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.cs
using 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.cs
using 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.cs
namespace 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.cs
namespace 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.cs
using 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

代码优先

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.cs
using 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.cs
using 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.cs
using 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