如何在 Entity Framework Core 中创建自引用实体？答案

【问题标题】：How do you create a self-referencing entity in Entity Framework Core?如何在 Entity Framework Core 中创建自引用实体？
【发布时间】：2017-03-21 00:37:27
【问题描述】：

我有一个类，Relationship，它有一个 InverseRelationship 属性。任何给定的关系总是有一个 InverseRelationship，它也是一个关系。

我的班级现在是这样的：

public class Relationship
{
    #region Constructor
    public Relationship()
    {

    }
    #endregion Constructor

    #region Properties
    [Key]
    [Required]
    public int Id { get; set; }
    [Required]
    public string Description { get; set; }
    public int? InverseRelationshipId { get; set; }

    #endregion Properties

    #region Related Properties
    [ForeignKey("InverseRelationshipId")]
    public virtual Relationship InverseRelationship { get; set; }

    #endregion Related Properties
}

当我尝试填充表格时，我收到一条消息说

Unable to save changes because a circular dependency was detected in the data to be saved

然后我尝试使用 Fluent API 来执行此操作，结果如下：

modelBuilder.Entity<Relationship>()
            .HasOne(r => r.InverseRelationship)
            .WithOne(r => r.InverseRelationship)
            .HasForeignKey<Relationship>(r => r.InverseRelationshipId)
            .IsRequired(false);

当我尝试创建迁移时，我得到以下信息：

The navigation property 'InverseRelationship' cannot be added to the entity type 'Relationship' because a navigation property with the same name already exists on entity type 'Relationship'.

这是有道理的，但我不知道如何绕过它。我不知道如何才能实现我在这里的目标。

更新这是我用来实际填充表格的代码（在尝试使用模型构建器代码之前）。

        EntityEntry<Relationship> rel1 = DbContext.Relationships.Add(new Relationship()
    {
        UserId = authorId,
        Title = "Relationship 1",
        Description = "Relationship 1",
        CreatedDate = createdDate,
        LastModifiedDate = lastModifiedDate
    });

    EntityEntry<Relationship> rel2 = DbContext.Relationships.Add(new Relationship()
    {
        UserId = authorId,
        Title = "Relationship 2",
        Description = "Relationship 2",
        CreatedDate = createdDate,
        LastModifiedDate = lastModifiedDate,
        InverseRelationship = rel1.Entity
    });

    EntityEntry<Relationship> rel3 = DbContext.Relationships.Add(new Relationship()
    {
        UserId = authorId,
        Title = "Relationship 3",
        Description = "Relationship 3",
        CreatedDate = createdDate,
        LastModifiedDate = lastModifiedDate
    });

    EntityEntry<Relationship> rel4 = DbContext.Relationships.Add(new Relationship()
    {
        UserId = authorId,
        Title = "Relationship 4",
        Description = "Relationship 4",
        CreatedDate = createdDate,
        LastModifiedDate = lastModifiedDate,
        InverseRelationship = rel3.Entity
    });

    rel1.Entity.InverseRelationship = rel2.Entity;
    rel3.Entity.InverseRelationship = rel4.Entity;

    DbContext.SaveChanges();

【问题讨论】：

这里的讨论和建议可能有用：github.com/aspnet/EntityFramework/issues/3376
你能发布代码吗？你是如何保存实体的？
@Smit 我将它添加到原始帖子中。我没有考虑到问题可能出在哪里，但现在你提到它可能是有道理的。

标签： c# entity-framework ef-code-first entity-framework-core

【解决方案1】：

感谢@Smit，我弄清楚了发生了什么。

显然，你需要调用

DbContext.SaveChanges();

在“关闭”循环引用中的圆之前。下面是工作代码。

    EntityEntry<Relationship> rel1 = DbContext.Relationships.Add(new Relationship()
{
    UserId = authorId,
    Title = "Relationship 1",
    Description = "Relationship 1",
    CreatedDate = createdDate,
    LastModifiedDate = lastModifiedDate
});

EntityEntry<Relationship> rel2 = DbContext.Relationships.Add(new Relationship()
{
    UserId = authorId,
    Title = "Relationship 2",
    Description = "Relationship 2",
    CreatedDate = createdDate,
    LastModifiedDate = lastModifiedDate,
    InverseRelationship = rel1.Entity
});

EntityEntry<Relationship> rel3 = DbContext.Relationships.Add(new Relationship()
{
    UserId = authorId,
    Title = "Relationship 3",
    Description = "Relationship 3",
    CreatedDate = createdDate,
    LastModifiedDate = lastModifiedDate
});

EntityEntry<Relationship> rel4 = DbContext.Relationships.Add(new Relationship()
{
    UserId = authorId,
    Title = "Relationship 4",
    Description = "Relationship 4",
    CreatedDate = createdDate,
    LastModifiedDate = lastModifiedDate,
    InverseRelationship = rel3.Entity
});

DbContext.SaveChanges();

rel1.Entity.InverseRelationship = rel2.Entity;
rel3.Entity.InverseRelationship = rel4.Entity;

DbContext.SaveChanges();

【讨论】：