实体框架的核心一对一的自参照关系失败

Question

在构建迁移我收到以下错误：

无法确定按类型“位置”的导航属性“Location.NorthLocation”表示的关系。要么手动配置关系，要么忽略模型中的该属性。

的位置实体：

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; } 

} 

类型配置：

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); 
    } 

} 

我的目标是有一个自我引用它自己的邻居到北部一个位置实体/南/东/西。

任何人都可以提出为什么我可能会得到这个错误？

Answer 1

您的模型配置不正确，因为它将每个导航属性都映射两次。例如。 SouthLocation被映射为NorthLocationId外键的逆向导航以及作为SouthLocationId的直接导航。

每个导航属性（即NorthLocation,SouthLocation,EastLocation,WestLocation）只能映射到一个关系（即在外键上）。

如果我删除关系配置部分的第2行和第4行，模型似乎是功能性的。

一般来说，在EF Core中，我们尝试通过让最后一个配置执行win来处理冲突的配置，但这有一些限制，很难预测执行此代码时可能发生的情况。当然，对于SQL Server使用EF Core 2.0 preview1，我得到了一个不同的异常（SQL Server的一个错误，抱怨cascade delte中的循环依赖），所以我们可以改进处理这种情况的方式。

这里是代码：

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; } 
    } 
}