Taking an example that is provided on the Fluent nHibernate website, I need to extend it slightly:

I need to add a 'Quantity' column to the StoreProduct table. How would I map this using nHibernate?

An example mapping is provided for the given scenario above, but I'm not sure how I would get the Quantity column to map to a property on the Product class:

public class StoreMap : ClassMap<Store>
{
  public StoreMap()
  {
    Id(x => x.Id);
    Map(x => x.Name);
    HasMany(x => x.Employee)
      .Inverse()
      .Cascade.All();
    HasManyToMany(x => x.Products)
     .Cascade.All()
     .Table("StoreProduct");
  }
}