Relationship Mapping in EF4 code-only CTP (when using inheritance?) - entity-framework

Question

I'm producing a simple composite patterned entity model using EF4 w/ the code-first CTP feature:
public abstract partial class CacheEntity
{
[Key]public string Hash { get; set; }
public string Creator { get; set; }
public int EntityType { get; set; }
public string Name { get; set; }
public string Predecessor { get; set; }
public DateTime DateTimeCreated { get; set; }
public virtual ICollection<CacheReference> References { get; set; }
}
public partial class CacheBlob : CacheEntity
{
public byte[] Content { get; set; }
}
public partial class CacheCollection : CacheEntity
{
public virtual ICollection<CacheEntity> Children { get; set; }
}
public class CacheReference
{
public string Hash { get; set; }
[Key]public string Reference { get; set; }
public virtual CacheEntity Entity { get; set; }
}
public class CacheEntities : DbContext
{
public DbSet<CacheEntity> Entities { get; set; }
public DbSet<CacheReference> References { get; set; }
}
Before I split out the primitive/collection derived classes it all worked nicely, but now I get this:
Unable to determine the principal end of the 'Cache.DataAccess.CacheEntity_References'
relationship. Multiple added entities may have the same primary key.
I figured that it may have been getting confused, so I thought I'd spell it out explicitly using the fluent interface, rather than the DataAnnotation attributes. Here's what I think defines the relationship properly:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<CacheEntity>().HasKey(ce => ce.Hash);
modelBuilder.Entity<CacheEntity>().HasOptional(ce => ce.References).WithMany();
modelBuilder.Entity<CacheReference>().HasKey(ce => ce.Reference);
modelBuilder.Entity<CacheReference>().HasRequired(cr => cr.Entity).WithOptional();
}
But I must be wrong, because now I get this:
Entities in 'CacheEntities.CacheReferenceSet' participate in the
'CacheReference_Entity' relationship. 0 related 'Entity' were found. 1 'Entity' is expected.
Various other ways of using the fluent API yield different errors, but nothing succeeds, so I am beginning to wonder whether these need to be done differently when I am using inheritance.
Any clues, links, ideas, guidance would be very welcome.

Answer 1

using the MapHierarchy works for me:
protected override void OnModelCreating(ModelBuilder builder){
builder.Entity<CacheBlob>().HasKey(b=> b.Hash).MapHierarchy();
}
As an example.
Further reference : http://blogs.msdn.com/b/efdesign/archive/2009/10/12/code-only-further-enhancements.aspx