Entity Framework Core 5 - 递归结构错误答案

【问题标题】：Entity Framework Core 5 - Error with recursive structureEntity Framework Core 5 - 递归结构错误
【发布时间】：2021-04-28 02:08:34
【问题描述】：

我正在尝试设置一个实体框架类，它有 4 个字段链接回相同类型的其他字段或为空。我的班级是这样的：

public class Patch : EntityBase
{
    [Key]
    public int PatchId { get; set; }

    [ForeignKey("NorthPatchId")]
    public virtual Patch NorthPatch { get; set; }

    [ForeignKey("SouthPatchId")]
    public virtual Patch SouthPatch { get; set; }

    [ForeignKey("EastPatchId")]
    public virtual Patch EastPatch { get; set; }

    [ForeignKey("WestPatchId")]
    public virtual Patch WestPatch { get; set; }
}

如果我只有 NorthPatch 和 SouthPatch，这可以正常工作，但是当我添加第三个 EastPatch 时，我在尝试进行迁移时收到以下错误：

System.InvalidOperationException: Unable to determine the relationship represented by navigation 'Patch.NorthPatch' of type 'Patch'.

【问题讨论】：

标签： entity-framework-core entity-framework-core-5

【解决方案1】：

这是一个非常酷的错误！我能够复制，并且作为奖励发现了报告的错误并且仍然对 EF Core 开放。

打开错误： https://github.com/dotnet/efcore/issues/21968

类似问题： Entity Framework Core One-One Self Referencing Relationship fails

解决方法： 删除 [ForeignKey] 属性，并将以下内容用于您的 OnModelConfiguring 作为您的上下文。

builder.Entity<Patch>()
    .HasOne(x => x.NorthPatch)
    .WithOne()
    .HasForeignKey(typeof(Patch), "NorthPatchId");

builder.Entity<Patch>()
    .HasOne(x => x.SouthPatch)
    .WithOne()
    .HasForeignKey(typeof(Patch), "SouthPatchId");

builder.Entity<Patch>()
    .HasOne(x => x.EastPatch)
    .WithOne()
    .HasForeignKey(typeof(Patch), "EastPatchId");

builder.Entity<Patch>()
    .HasOne(x => x.WestPatch)
    .WithOne()
    .HasForeignKey(typeof(Patch), "WestPatchId");

【讨论】：

【解决方案2】：

@Lucutah 在我写的时候回答了这个问题，但我想发布这个我发现值得一看的其他解决方案。它具有类似的结果，但也会自动维护东/西和北/南条目之间的关系。虽然这可能远不及性能，具体取决于您要执行的操作。

public class Patch : EntityBase
{
    public int PatchId { get; set; }
    public virtual Patch NorthPatch { get; set; }
    public virtual Patch SouthPatch { get; set; }
    public virtual Patch EastPatch { get; set; }
    public virtual Patch WestPatch { get; set; }
}

在上下文中..

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Patch>().HasKey("PatchId");

        modelBuilder.Entity<Patch>()
           .HasOne(x => x.NorthPatch)
           .WithOne(x => x.SouthPatch)
           .HasForeignKey(typeof(Patch), "NorthPatchId");
        modelBuilder.Entity<Patch>()
           .HasOne(x => x.EastPatch)
           .WithOne(x => x.WestPatch)
           .HasForeignKey(typeof(Patch), "EastPatchId");
    }

【讨论】：