您如何在Entity Framework Core中创建自引用实体？

Question

I have a class, Relationship, that will have an InverseRelationship property. Any given Relationship will always have exactly one InverseRelationship which is also a Relationship.

My class looks like this right now:

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
}

When I try to populate the table, I get a message saying

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

So then I tried to use Fluent API to do this, and I ended up with the following:

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

And when I try to create a migration, I get the following:

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'.

That makes sense, but I don't know how to get around it. I'm at a loss for how I can achieve what I'm going for here.

Update Here is the code that I used to actually populate the table (prior to trying to use model builder code).

        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();

Answer 1

Thanks to @Smit, I figured out what was going on.

Apparently, you need to call

DbContext.SaveChanges();

Before 'closing' the circle in the circular reference. Below is working code.

    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();