EF 4.1 RC Many to many relationship in EF CF

Question

I have two entities with many to many relationship like this:

class author
{
  public int AuthorID{get;set;}
  public string Name{get;set;}
  public virtual ICol         


        

Answer 1

This was problematic with EDMX but with EF 4.1 fluent API you can map it:

modelBuilder.Entity<book>()
            .HasMany(b => b.authors)
            .WithMany(a => a.books)
            .Map(m => m.MapLeftKey("BookID")
                   .MapRightKey("AuthorID")
                   .ToTable("BookAuthor"));

As you can see I don't map BookAuthor column. That column is unknown to EF and must be auto incremented.

This obviously can't work with a Code-first approach but only if you use Fluent API against existing database.

Answer 2

I don't think EF allows you to have a separate Id in many-to-many junction tables.

The alternative is just mapping BookAuthor as an entity.

On a side note, NHibernate supports this construct using an idbag