无法确定导航属性ASP.NET核心2.0实体框架所代表的关系

Question

我目前正在开发一个使用EntityFramework的ASP.NET应用程序,用于给定的代码

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:

无法确定类型为"ICollection"的导航属性"EnumMeta.Messages"所代表的关系.手动配置关系,或使用'[NotMapped]'属性或在'OnModelCreating'中使用'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核心2.0项目,以对数据库执行"代码优先"方法.

我已经尝试过设置[ForeignKey("MessageMeta")]上面public virtual ICollection<MessageMeta> Messages { get; set; }没有任何积极的解决方案.

Answer 1

正如我之前评论的那样,Entity Framework和之间存在很多差异Entity Framework Core 2.0,我认为你不能只使用生成的模型Entity Framework并运行Code First Entity Framework Core 2.0.

从所描述的模型来看,它看起来像MessageMeta并且EnumMeta具有多对多的关系.

直至今日,Entity Framework Core 2.0依然不支持多到许多没有中间阶级.所以为了做多对多EF Core 2.0,你需要中间类.

MessageMeta

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; }
    }
}

EnumMeta

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; }
    }
}

的DbContext

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?}");
            });
        }
    }
}

要运行的命令 Package Manager Console

Add-Migration Init
Update-Database

生成的数据库