A.net core 2.0新特性支持通过IEntityTypeConfiguration<>添加Code First配置到一个封装类。
新建目标框架为.NET Core类库
新建完了以后右键点击程序集，选择属性，选择目标框架为.NET Core 2.0
在EntityFrameworkCore程序集中添加类User（用户）、Address（用户住址）、Book（书）、Author（作者）。这里不讨论各个类设计的合理性和程序架构，主要目的是为了演示各个类之间的关系配置。
User和Address类用于演示配置1-0..1关系。User和Book用于演示1-N，即1对多关系。Book和Author用于演示N-N关系，即多对多关系。
注意：在EF6.x中，当配置1-0..1关系时，附属表的主键值可以与主表的主键相同，主表对应这里的User,附属表对应Address，而由于篇幅有限，在.net core 2.0中不讨论此实现，即每个表都有自己的主键，表关联都通过外键作为实现。
User表实现如下
usingSystem;namespaceEntityFrameworkCore{/// <summary>/// 用户模型/// </summary>publicsealedclassUser{publicUser(){ ID =Guid.NewGuid();TimeCreated=DateTime.Now;}publicGuid ID {get;privateset;}/// <summary>/// 用户名称/// </summary>publicstringName{get;set;}/// <summary>/// 用户登录密码/// </summary>publicstringPassword{get;set;}/// <summary>/// 用户创建时间/// </summary>publicDateTimeTimeCreated{get;privateset;}publicAddressAddress{get;set;}}}
Address表实现如下
using System;namespace EntityFrameworkCore
{
///
/// 用户地址模型
///
public sealed class Address
{
public Address()
{
ID = Guid.NewGuid();
TimeCreated = DateTime.Now;
}
public Guid ID { get; private set; } ///
/// 国家
///
public string Country { get; set; } ///
/// 省
///
public string Province { get; set; } ///
/// 城市
///
public string City { get; set; } ///
/// 区/县
///
public string Area { get; set; } ///
/// 街道
///
public string Street { get; set; } ///
/// 创建时间
///
public DateTime TimeCreated { get; private set; } ///
/// 用户ID
///
public Guid UserID { get; set; } public User User { get; set; }
}
}
Book实现如下
using System;
using System.Collections.Generic;namespace EntityFrameworkCore
{
///
/// 书模型
///
public sealed class Book
{
public Book()
{
ID = Guid.NewGuid();
TimeCreated = DateTime.Now;
} public Guid ID { get; private set; }
public DateTime TimeCreated { get; private set; }
///
/// 书名
///
public string Name { get; set; } ///
/// 出版号
///
public string PublicNo { get; set; } public List Authors { get; set; }
}
}
Author实现如下
using System;
using System.Collections.Generic;namespace EntityFrameworkCore
{
///
/// 作者模型
///
public sealed class Author
{
public Author()
{
ID = Guid.NewGuid();
TimeCreated = DateTime.Now;
} public Guid ID { get; private set; } public DateTime TimeCreated { get; private set; } ///
/// 作者名字
///
public string Name { get; set; } public List Books { get; set; }
}
}
点击工具->NuGet包管理器->程序包管理控制台，在程序包管理控制台中输入命令：Install-Package Microsoft.EntityFrameworkCore.SqlServer
在EntityFrameworkCore中添加文件夹ModelConfigs
1-0..1关系配置User—Address：
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;namespace EntityFrameworkCore.ModelConfigs
{
public sealed class UserConfig:IEntityTypeConfiguration
{
public void Configure(EntityTypeBuilder builder)
{
builder.HasKey(q => q.ID);
builder.Property(q => q.Name).HasMaxLength().IsRequired();
builder.Property(q => q.Password).HasMaxLength().IsRequired();
builder.Property(q => q.TimeCreated).IsRequired(); //使用HasOne和WithOne两个扩展方法对User表和Address表进行1-1关系配置
builder.HasOne(q => q.Address).WithOne(q => q.User).HasForeignKey
(q => q.UserID);
}
}
}
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;namespace EntityFrameworkCore.ModelConfigs
{
public sealed class AddressConfig: IEntityTypeConfiguration
{
public void Configure(EntityTypeBuilder
builder)
{
builder.HasKey(q => q.ID);
builder.Property(q => q.Area).HasMaxLength().IsRequired();
builder.Property(q => q.City).HasMaxLength().IsRequired();
builder.Property(q => q.Country).HasMaxLength().IsRequired();
builder.Property(q => q.Province).HasMaxLength().IsRequired();
builder.Property(q => q.Street).HasMaxLength().IsRequired();
builder.Property(q => q.TimeCreated).IsRequired();
builder.Property(q => q.UserID).IsRequired();
}
}
}
UserConfig和AddressConfig分别对User表数据和Address表数据进行了配置，添加FluentApiDemoDbContext类并继承DbContext，微软官方解释DbContext实例是一个带有数据库的会话并且能用于添加和查询实体。FluentApiDemoDbContext类代码如下：
using System;
using System.Linq;
using System.Reflection;
using Microsoft.EntityFrameworkCore;namespace EntityFrameworkCore
{
public class FluentApiDemoDbContext : DbContext
{
public FluentApiDemoDbContext(DbContextOptions options) : base(options)
{
} public DbSet User { get; set; } public DbSet
Address { get; set; } protected override void OnModelCreating(ModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder); var typesToRegister = Assembly.GetExecutingAssembly().GetTypes()
.Where(q => q.GetInterface(typeof(IEntityTypeConfiguration<>).FullName) != null); foreach (var type in typesToRegister)
{ dynamic configurationInstance = Activator.CreateInstance(type);
modelBuilder.ApplyConfiguration(configurationInstance);
} }
}
}
如果这里直接把EntityFrameworkCore设为启动项，当在程序包管理控制台中输入：Update-Database时将报错：Unable to create an object of type ‘FluentApiDemoDbContext’. Add an implementation of ‘IDesignTimeDbContextFactory<FluentApiDemoDbContext>’ to the project, or seehttps://go.microsoft.com/fwlink/?linkid=851728for additional patterns supported at design time.提示需要添加一个IDesignTimeDbContextFactory<FluentApiDemoDbContext>的实现，这里如果是用Console写Demo，那么可以自行实现该接口，在该文中我将添加WebApi作为启用项。Startup.cs内容如下：
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using EntityFrameworkCore;namespace WebApi
{
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
} public 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.AddMvc();
var connection = @”Server=(localdb)\mssqllocaldb;Database=FluentApiDemoDb;Trusted_Connection=True;”;
services.AddDbContextPool(options => options.UseSqlServer(connection));
} // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
} app.UseMvc();
}
}
}
配置以后将该WebApi项目设置为启动项，在程序包管理控制台中输入：Add-Migration Initial以启动迁移。完成以后，项目会添加Migraions文件夹，
在程序包管理控制台中输入：Update-Database以完成数据迁移。完成后打开：视图->SQL Server对象资源管理器，可以查看比较具体的数据结构。
这里着重要看Address表中的UserID,UserID做为Address表的外键是非空的，按照文章开头说的1-0..1关系，这里只实现了1-1，并没有实现1-0关系，更改AddressConfig中的关系配置为：
…
builder.HasOne(q => q.User).WithOne(q => q.Address).HasForeignKey<Address>(q => q.UserID).IsRequired(false);
并更改Address中的代码为：
…
public Guid? UserID { get; set; }
添加迁移并更新到数据库
1-N关系配置，1个用户拥有多本书。在User表中添加
…
public List<Book> Books { get; set; }
Book表中添加
…
public Guid? UserID { get; set; }
public User User { get; set; }
在ModelConfigs中添加BookConfig
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;namespace EntityFrameworkCore.ModelConfigs
{
public sealed class BookConfig: IEntityTypeConfiguration
{
public void Configure(EntityTypeBuilder builder)
{
builder.HasKey(q => q.ID);
builder.Property(q => q.Name).HasMaxLength().IsRequired();
builder.Property(q => q.PublicNo).HasMaxLength().IsRequired(); builder.HasOne(q => q.User).WithMany(q => q.Books).HasForeignKey(q => q.UserID).IsRequired(false);
}
}
}
在FluentApiDemoDbContext中注册实体
…
public DbSet<Book> Book { get; set; }
在程序包管理控制台中添加迁移并更新到数据库：
N-N关系配置，当使用EF6.x时，配置多对多关系，EF会自动生成中间表，在.net core中，需要手动添加关系表，实际上在EF6.x中当配置多对多关系时，也可以通过中间表配置1对多的方式实现多对多。
这里通过Book表和Author表实现多对多关系配置。一个作者可以有多本书，一本书有多个作者。
首先添加关系表AuthorsInBooks
using System;namespace EntityFrameworkCore
{
public sealed class AuthorsInBooks
{
public Guid BookID { get; set; }
public Book Book { get; set; } public Guid AuthorID { get; set; } public Author Author { get; set; }
}
}
同时更改Books表
public List<Author> Authors { get; set; }改为public List<AuthorsInBooks> AuthorsInBooks { get; set; }
同理更改Author表
public List<Book> Books { get; set; }改为 public List<AuthorsInBooks> AuthorsInBooks { get; set; }
添加AuthorsConfig
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;namespace EntityFrameworkCore.ModelConfigs
{
public sealed class AuthorConfig:IEntityTypeConfiguration
{
public void Configure(EntityTypeBuilder builder)
{
builder.HasKey(q => q.ID);
builder.Property(q => q.Name).HasMaxLength().IsRequired();
builder.Property(q => q.TimeCreated).IsRequired();
}
}
}
并在FluentApiDemoDbContext中注册Author
…
public DbSet<Author> Author { get; set; }
接下来添加AuthorsInBooksConfig
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;namespace EntityFrameworkCore.ModelConfigs
{
public sealed class AuthorsInBooksConfig:IEntityTypeConfiguration
{
public void Configure(EntityTypeBuilder builder)
{
builder.HasKey(q => new
{
q.AuthorID,
q.BookID
}); builder.HasOne(q => q.Author).WithMany(q => q.AuthorsInBooks).HasForeignKey(q => q.AuthorID);
builder.HasOne(q => q.Book).WithMany(q => q.AuthorsInBooks).HasForeignKey(q => q.BookID);
}
}
}
在管理控制台中添加迁移并更新到数据库
