在 table 上引入 FOREIGN KEY 约束可能会导致引用自身的 class 出现循环或多个级联路径

Question

我在尝试更新包含引用自身的 class 的数据库时收到错误 Introducing FOREIGN KEY constraint 'FK_Company_Company_ParentId' on table 'Company' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.。

Class 产生问题：

    public class Company
    {
        public Country Country { get; set; }
        [Required]
        public int CountryId { get; set; }
        [Required]
        public int Id { get; set; }
        [Required]
        public string Name { get; set; }
        public Company Parent { get; set; }
        public int ParentId { get; set; }
    }

我的 dbcontext 看起来像这样：

using System;
using System.Collections.Generic;
using System.Text;
using ArtGalleries.Domain;
using Microsoft.EntityFrameworkCore;

namespace ArtGalleries.Data
{
    public class ArtGalleriesContext:DbContext
    {
        public ArtGalleriesContext(DbContextOptions<ArtGalleriesContext> options):base(options)
        {

        }

        public DbSet<ArtItem> ArtItems { get; set; }
        public DbSet<Artist> Artists { get; set; }
        public Company Companies { get; set; }
        public DbSet<Floor> Floors { get; set; }
        public Location Locations { get; set; }
        public DbSet<Room> Rooms { get; set; }
        public DbSet<User> Users { get; set; }






        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<UserLocation>()
                .HasKey(u => new {u.UserId, u.LocationId});
            //modelBuilder.Entity().
            //modelBuilder.Entity<Company>()
            //    .HasOne(c => c.Company)
            //    .WithOne(pc => pc.Company)
            //    .HasForeignKey(fk => fk.ParentId);
        }
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured)
            {
                optionsBuilder.UseSqlServer(
                    "Server=(localdb)\mssqllocaldb;Database=GalleriesDB;Trusted_Connection=True;");
            }
        }
    }
}

注意：评论的文字是我试图解决这个问题，但没有结果，因为我遇到了语法错误。

Answer 1

对于 EF Core 中的自引用，您应该将 ParentId 设置为 Nullable 并使用 ForeignKey 来配置哪个属性应该用作外键属性对于如下所示的给定关系：

public class Company
{
    [Required]
    public int Id { get; set; }

    [Required]
    public string Name { get; set; }


    public int? ParentId { get; set; }
    [ForeignKey("ParentId")]
    public Company Parent { get; set; }

    [Required]
    public int CountryId { get; set; }
    [ForeignKey("CountryId ")]
    public Country Country { get; set; }

}

在 table 上引入 FOREIGN KEY 约束可能会导致引用自身的 class 出现循环或多个级联路径

Introducing FOREIGN KEY constraint on table may cause cycles or multiple cascade paths for a class that references itself

c#

asp.net-core-webapi

ef-core-2.2