无法确定导航属性 ASP.NET core 2.0 Entity Framework 表示的关系

Question

我目前正在为给定的代码开发一个使用 EntityFramework 的 ASP.NET 应用程序

public partial class EnumMeta : Meta
{
    public EnumMeta()
    {
        this.Messages = new HashSet<MessageMeta>();
    }

    public bool IsFlag { get; set; }

    public virtual ICollection<MessageMeta> Messages { get; set; }
}

public partial class MessageMeta : Meta
{
    public MessageMeta()
    {
        this.Enums = new HashSet<EnumMeta>();
        this.Receiver = new HashSet<Module>();
        this.Sender = new HashSet<Module>();
    }

    public int MsgId { get; set; }

    public virtual ICollection<EnumMeta> Enums { get; set; }
    public virtual ICollection<Module> Receiver { get; set; }
    public virtual ICollection<Module> Sender { get; set; }
}

我收到一个错误：

无法确定“ICollection”类型的导航属性“EnumMeta.Messages”表示的关系。手动配置关系，或使用“[NotMapped]”属性或使用“OnModelCreating”中的“EntityTypeBuilder.Ignore”忽略此属性。

此代码由 EntityFramework 使用 WPF 项目自动生成，然后将模型带到 ASP.NET core 2.0 项目以对数据库执行“代码优先”方法。

我已经尝试在public virtual ICollection<MessageMeta> Messages { get; set; }上方设置[ForeignKey("MessageMeta")]，但没有任何积极的解决方案。

Answer 1

正如我之前所说，Entity Framework 和 Entity Framework Core 2.0 之间存在许多差异，我认为您不能只使用从 Entity Framework 生成的模型并使用 Entity Framework Core 2.0 运行 Code First。

从描述的模型来看，MessageMeta 和 EnumMeta 似乎具有多对多关系。

直到今天，Entity Framework Core 2.0 仍然不支持多对多没有中间类。所以为了在EF Core 2.0做多对多，你需要中间类。

消息元

using System.Collections.Generic;

namespace DL.SO.MessageEnum.Web.UI.Models
{
    public class MessageMeta
    {
        public int MsgId { get; set; }

        public List<MessageEnum> EnumMetas { get; set; }
    }
}

枚举元

using System.Collections.Generic;

namespace DL.SO.MessageEnum.Web.UI.Models
{
    public class EnumMeta
    {
        public int EnumId { get; set; }
        public bool IsFlag { get; set; }

        public List<MessageEnum> MessageMetas { get; set; }
    }
}

MessageEnum（或者你可以称之为EnumMessage）——中间模型

namespace DL.SO.MessageEnum.Web.UI.Models
{
    public class MessageEnum
    {
        public int MessageMetaId { get; set; }
        public MessageMeta MessageMeta { get; set; }

        public int EnumMetaId { get; set; }
        public EnumMeta EnumMeta { get; set; }
    }
}

数据库上下文

using Microsoft.EntityFrameworkCore;

namespace DL.SO.MessageEnum.Web.UI.Models
{
    public class AppDbContext : DbContext
    {
        public AppDbContext(DbContextOptions<AppDbContext> options): base(options) { }

        public DbSet<MessageMeta> Messages { get; set; }
        public DbSet<EnumMeta> Enums { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<MessageMeta>()
                .HasKey(x => x.MsgId);

            modelBuilder.Entity<EnumMeta>()
                .HasKey(x => x.EnumId);

            modelBuilder.Entity<MessageEnum>()
                .HasKey(x => new { x.MessageMetaId, x.EnumMetaId });
            modelBuilder.Entity<MessageEnum>()
                .HasOne(x => x.MessageMeta)
                .WithMany(m => m.EnumMetas)
                .HasForeignKey(x => x.MessageMetaId);
            modelBuilder.Entity<MessageEnum>()
                .HasOne(x => x.EnumMeta)
                .WithMany(e => e.MessageMetas)
                .HasForeignKey(x => x.EnumMetaId);
        }
    }
}

appsettings.json

{
  "ConnectionStrings": {
    "AppDbConnection": "Data Source=.\\SQLEXPRESS;Initial Catalog=SO.MessageEnum;Integrated Security=True;MultipleActiveResultSets=False;"
  },
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Warning"
    }
  }
}

启动

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using DL.SO.MessageEnum.Web.UI.Models;
using Microsoft.EntityFrameworkCore;

namespace DL.SO.MessageEnum.Web.UI
{
    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)
        {
            string dbConnectionString = Configuration.GetConnectionString("AppDbConnection");

            services.AddDbContext<AppDbContext>(options =>
                options.UseSqlServer(dbConnectionString)
            );

            services.AddMvc();
        }

        // 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.UseBrowserLink();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
            }

            app.UseStaticFiles();

            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            });
        }
    }
}

在Package Manager Console 上运行的命令

Add-Migration Init
Update-Database

生成的数据库