Entity Framework 4.1 Code First: Many to many with ICollection on only one entity

Question

Given these classes, using EF 4.1 Code First, this will (by convention) leave to a many-to-many relation between Page and Tag:

public interface ITaggable
{
  ICollection<Tag> { get; set; }
}

public class Page : ITaggable
{
  public virtual ICollection<Tag> { get; set; }
}

public class Tag
{
  public virtual ICollection<Page> { get; set; }
}

Since I have a bunch of other classes, that implement the ITaggable I'd have to add all these collections to Tag:

public class Tag
{
  public virtual ICollection<Page> { get; set; }
  public virtual ICollection<Post> { get; set; }
  public virtual ICollection<Event> { get; set; }
  ...
}

If I leave out these properties on Tag EF generates a 1-to-many relation. Is there a way to leave out the ICollection<T> on Tag and get a many-to-many relation anyway?

(Remark: ICollection<ITaggable> on Tag doesn't work.)

Answer 1

You have to use fluent mapping:

public interface ITaggable
{
  ICollection<Tag> { get; set; }
}

public class Page : ITaggable
{
    ...
    public virtual ICollection<Tag> Tags { get; set; }
}

public class Tag
{
    ...
}

public class Context : DbContext
{
    public DbSet<Tag> Tags { get; set; }
    public DbSet<Page> Pages { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Page>()
                    .HasMany(p => p.Tags)
                    .WithMany();
    }
}