Entity Framework 核心一对一自引用关系失败

Question

构建迁移时出现以下错误：

无法确定类型 'Location' 的导航属性 'Location.NorthLocation' 表示的关系。手动配置关系，或从模型中忽略此属性。

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);
    }

}

我的目标是拥有一个 Location 实体，该实体将自己的邻居自引用到 north/south/east/west。

谁能告诉我为什么会出现此错误？

Answer 1

您的模型配置不正确，因为它将每个导航属性映射了两次。例如。 SouthLocation 被映射为 NorthLocationId 外键的反向导航和 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（即到一个外国钥匙）。

如果我删除关系配置部分的第 2 行和第 4 行，模型似乎可以正常运行。

一般来说，在 EF Core 中，我们试图通过让最后的配置执行来处理配置冲突，但这有一些局限性，很难预测执行这段代码时会发生什么。当然，针对 SQL 服务器使用 EF Core 2.0 preview1，我得到了一个不同的异常（一个错误形式 SQL 服务器，抱怨级联删除中的循环依赖），所以我们可能改进了我们的方式处理这种情况。

代码如下：


    using System;
    using Microsoft.EntityFrameworkCore;
    using Microsoft.EntityFrameworkCore.Metadata;

    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; }
        }
    }

Answer 2

我只需将 .HasOne() 添加到主模型就可以解决同样的问题

    // Locations
    builder.Entity<Location>().HasOne(x => x.NorthLocation);
    builder.Entity<Location>().HasOne(x => x.SouthLocation);
    builder.Entity<Location>().HasOne(x => x.EastLocation);
    builder.Entity<Location>().HasOne(x => x.WestLocation);

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