# 数据访问和代码优先
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();
}
}
}
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//appsettings.json
{
"ConnectionStrings": {
"Enable": "MySQL",
"MySql": "Server=localhost;User Id=root;Password=123456;Database=meowv_blog_tutorial",
"SqlServer": "",
"PostgreSql": "",
"Sqlite": ""
}
}
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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));
...
}
}
}
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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);
}
}
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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;
}
});
}
}
}
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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<int>。关于这点可以参考ABP文档，https://docs.abp.io/zh-Hans/abp/latest/Entities (opens new window)
点击查看代码
//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; }
}
}
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//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; }
}
}
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//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; }
}
}
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//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; }
}
}
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//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; }
}
}
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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; }
...
}
...
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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_";
}
}
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//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";
}
}
}
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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 (opens new window)
//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();
});
}
}
}
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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>();
}
}
}
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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();
}
}
}
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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"
}
}
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//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();
}
}
}
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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
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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？😁😁😁