Fluent API中的父子关系

Question

Okay, this is getting ridiculous as this is turning out to be much more difficult than it has any right to be.

If I use my original code with no FluentAPI mapping, I have a ParentID field which is not used, and a new field called Node_ID is used.

public class Node {
  public long ID { get; private set; }
  public long ParentID { get; set; }
  public ICollection<Node> Children { get; set; }
}

Here are my various attempts:

protected override void OnModelCreating(DbModelBuilder mb)
{
  mb.Entity<Node>()
    .HasMany<Node>(h => h.Children)
    .WithOptional()
    .HasForeignKey(h => h.ParentID);
}

DbUpdateException: Unable to determine a valid ordering for dependent operations. Dependencies may exist due to foreign key constraints, model requirements, or store-generated values.

protected override void OnModelCreating(DbModelBuilder mb)
{
  mb.Entity<Node>()
    .HasMany<Node>(h => h.Children)
    .WithOptional()
    .Map(m => m.MapKey("ParentID"));
}

MetadataException: Schema specified is not valid. Errors: (82,6) : error 0019: Each property name in a type must be unique. Property name 'ParentID' was already defined.

[ForeignKey("ParentID")]
public ICollection<Node> Children { get; set; }

protected override void OnModelCreating(DbModelBuilder mb)
{
  mb.Entity<Node>()
    .HasMany<Node>(h => h.Children)
    .WithOptional()
}

DbUpdateException: Unable to determine a valid ordering for dependent operations. Dependencies may exist due to foreign key constraints, model requirements, or store-generated values.

Update

Using the Fluent API code from my first attempt code above (.HasForeignKey), and by making ParentID nullable (public long? ParentID), I have gotten the database to successfully map. Is there any way to do this without making the FK nullable? I would like the key to be 0 when no parent exists. If not, oh well, I will deal.

Answer 1

没有办法避免可为空的ParentId您告诉EF父对象是可选的（否则必须不可以使用该表），并且因为相关的FK属性必须可为空。