實體框架的核心一對一的自參照關係失敗

Question

在構建遷移我收到以下錯誤：

無法確定按類型「位置」的導航屬性「Location.NorthLocation」表示的關係。要麼手動配置關係，要麼忽略模型中的該屬性。

的位置實體：

public class Location 
{ 
    public Guid Id { get; set; } 

    public DateTime CreatedWhen { get; set; } 
    public string CreatedBy { get; set; } 
    public DateTime ModifiedWhen { get; set; } 
    public string ModifiedBy { get; set; } 

    public Guid? NorthLocationId { get; set; } 
    public virtual Location NorthLocation { get; set; } 

    public Guid? SouthLocationId { get; set; } 
    public virtual Location SouthLocation { get; set; } 

    public Guid? EastLocationId { get; set; } 
    public virtual Location EastLocation { get; set; } 

    public Guid? WestLocationId { get; set; } 
    public virtual Location WestLocation { get; set; } 

} 

類型配置：

public class MyContext : DbContext 
{ 
    public MyContext(DbContextOptions<MyContext> options) : base(options) 
    { 
    } 

    public DbSet<Location> Locations { get; set; } 

    protected override void OnModelCreating(ModelBuilder builder) 
    { 
     base.OnModelCreating(builder); 

     builder.Entity<T>().HasKey("Id"); 
     builder.Entity<T>().Property("Id").ValueGeneratedOnAdd(); 
     builder.Entity<T>().Property("CreatedWhen").HasDefaultValueSql("GETDATE()").ValueGeneratedOnAdd(); 
     builder.Entity<T>().Property("ModifiedWhen").IsRequired(); 
     builder.Entity<T>().Property("CreatedBy").HasMaxLength(50).IsRequired(); 
     builder.Entity<T>().Property("ModifiedBy").HasMaxLength(50).IsRequired(); 

     // Locations 
     builder.Entity<Location>().HasOne(x => x.NorthLocation).WithOne(x => x.SouthLocation).HasForeignKey(typeof(Location), "NorthLocationId").OnDelete(DeleteBehavior.SetNull); 
     builder.Entity<Location>().HasOne(x => x.SouthLocation).WithOne(x => x.NorthLocation).HasForeignKey(typeof(Location), "SouthLocationId").OnDelete(DeleteBehavior.SetNull); 
     builder.Entity<Location>().HasOne(x => x.EastLocation).WithOne(x => x.WestLocation).HasForeignKey(typeof(Location), "EastLocationId").OnDelete(DeleteBehavior.SetNull); 
     builder.Entity<Location>().HasOne(x => x.WestLocation).WithOne(x => x.EastLocation).HasForeignKey(typeof(Location), "WestLocationId").OnDelete(DeleteBehavior.SetNull); 
    } 

} 

我的目標是有一個自我引用它自己的鄰居到北部一個位置實體/南/東/西。

任何人都可以提出爲什麼我可能會得到這個錯誤？

Answer 1

您的模型配置不正確，因爲它將每個導航屬性都映射兩次。例如。 SouthLocation被映射爲NorthLocationId外鍵的逆向導航以及作爲SouthLocationId的直接導航。

每個導航屬性（即NorthLocation,SouthLocation,EastLocation,WestLocation）只能映射到一個關係（即在外鍵上）。

如果我刪除關係配置部分的第2行和第4行，模型似乎是功能性的。

一般來說，在EF Core中，我們嘗試通過讓最後一個配置執行win來處理衝突的配置，但這有一些限制，很難預測執行此代碼時可能發生的情況。當然，對於SQL Server使用EF Core 2.0 preview1，我得到了一個不同的異常（SQL Server的一個錯誤，抱怨cascade delte中的循環依賴），所以我們可以改進處理這種情況的方式。

這裏是代碼：

using System; 使用Microsoft.EntityFrameworkCore;使用Microsoft.EntityFrameworkCore.Metadata的 ;

namespace ConsoleApp4 
{ 
    class Program 
    { 
     static void Main(string[] args) 
     { 
      using (var db = new MyContext()) 
      { 
       db.Database.EnsureDeleted(); 
       db.Database.EnsureCreated(); 
      } 
     } 
    } 

    public class MyContext : DbContext 
    { 
     public DbSet<Location> Locations { get; set; } 
     protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) 
     { 
      optionsBuilder.UseSqlServer(@"server=(localdb)\mssqllocaldb;database=hey;ConnectRetryCount=0"); 
     } 

     protected override void OnModelCreating(ModelBuilder modelBuilder) 
     { 
      modelBuilder.Entity<Location>().HasKey("Id"); 
      modelBuilder.Entity<Location>().Property("Id").ValueGeneratedOnAdd(); 
      modelBuilder.Entity<Location>().Property("CreatedWhen").HasDefaultValueSql("GETDATE()").ValueGeneratedOnAdd(); 
      modelBuilder.Entity<Location>().Property("ModifiedWhen").IsRequired(); 
      modelBuilder.Entity<Location>().Property("CreatedBy").HasMaxLength(50).IsRequired(); 
      modelBuilder.Entity<Location>().Property("ModifiedBy").HasMaxLength(50).IsRequired(); 
      modelBuilder.Entity<Location>().HasOne(x => x.NorthLocation).WithOne(x => x.SouthLocation).HasForeignKey(typeof(Location), "NorthLocationId").OnDelete(DeleteBehavior.Restrict); 
      modelBuilder.Entity<Location>().HasOne(x => x.EastLocation).WithOne(x => x.WestLocation).HasForeignKey(typeof(Location), "EastLocationId").OnDelete(DeleteBehavior.Restrict); 
     } 
    } 

    public class Location 
    { 
     public Guid Id { get; set; } 
     public DateTime CreatedWhen { get; set; } 
     public string CreatedBy { get; set; } 
     public DateTime ModifiedWhen { get; set; } 
     public string ModifiedBy { get; set; } 
     public Guid? NorthLocationId { get; set; } 
     public virtual Location NorthLocation { get; set; } 
     public Guid? SouthLocationId { get; set; } 
     public virtual Location SouthLocation { get; set; } 
     public Guid? EastLocationId { get; set; } 
     public virtual Location EastLocation { get; set; } 
     public Guid? WestLocationId { get; set; } 
     public virtual Location WestLocation { get; set; } 
    } 
}