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

Question

Hi Everyone,

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