使用 Entity Framework Core 5 的自引用表

Question

我的应用中有一个自引用实体。与其他包类型具有依赖关系（作为列表）的包类型。我正在尝试使用模型构建器设计所需的中间表。不幸的是，我无法正确填写密钥。

System.InvalidOperationException: '无法跟踪'PackageDependency (Dictionary)' 类型的实体，因为它的主键属性'DependencyId' 为空。'

    public class PackageType
    {
        [Key]
        public String Tag { get; set; }

        public virtual List<PackageType> Dependencies { get; set; } = new List<PackageType>();
    }

数据库上下文：

 protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<PackageType>()
                .HasMany(p => p.Dependencies)
                .WithMany(p => p.Dependencies)
                .UsingEntity<Dictionary<string, object>>(
                    "PackageDependency",
                    j => j
                        .HasOne<PackageType>()
                        .WithMany()
                        .HasForeignKey("PackageId")
                        .HasConstraintName("FK_PackageDependency_PackageId")
                        .OnDelete(DeleteBehavior.Cascade),
                    j => j
                        .HasOne<PackageType>()
                        .WithMany()
                        .HasForeignKey("DependencyId")
                        .HasConstraintName("FK_PackageDependency_DependencyId")
                        .OnDelete(DeleteBehavior.ClientCascade),
                    e => e.HasKey("PackageId", "DependencyId"));
        }

有人给我提示吗？

非常感谢！

Answer 1

我很惊讶 EF Core 竟然允许这样做

.HasMany(p => p.Dependencies)
.WithMany(p => p.Dependencies)

（对关系的双方使用同一个集合）而不报告错误。

Many-to-many 需要 2 个集合导航属性 - 关系的每一侧一个。因此，即使这是自引用关系，它仍然需要 2 个单独的集合导航属性绑定到相应的连接实体 FK。例如

public virtual List<PackageType> ChildDependencies { get; set; } = new List<PackageType>();
public virtual List<PackageType> ParentDependencies { get; set; } = new List<PackageType>();

和

.HasMany(p => p.ChildDependencies) // -> j.PackageId
.WithMany(p => p.ParentDependencies) // -> j.DependencyId

Answer 2

你需要两个参考，一个是向上的，另一个是向下的：

public class PackageType
{
    [Key]
    public String Tag { get; set; }

    public ICollection<PackageDependency> Dependents { get; set; }
    public ICollection<PackageDependency> Pendents { get; set; }
}

public class PackageDependency
{
    public string DependentTag { get; set; }
    public PackageType Dependend { get; set }
    public string PendentTag { get; set; }
    public PackageType Pendend { get; set; }
}


protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<PackageDependency>()
            .HasKey(r => new { r.DependentTag, r.PendentTag });
    modelBuilder.Entity<PackageDependency>()
        .HasOne(r => r.Pendend)
        .WithMany(p => p.Dependents)
        .IsRequired()
        .OnDelete(DeleteBehavior.NoAction);
    modelBuilder.Entity<PackageDependency>()
        .HasOne(r => r.Dependend)
        .WithMany(d => d.Pendents)
        .IsRequired()
        .OnDelete(DeleteBehavior.NoAction);
}