基于 abp vNext 和 .NET Core 开发博客项目 - 数据访问和代码优先 / 四六文摘

系列文章

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。

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

点击查看代码

//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

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.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？

基于 abp vNext 和 .NET Core 开发博客项目 - 数据访问和代码优先

系列文章

数据访问

代码优先

相关推荐