Combine RESTful routes with DataMapper

Hi

I am writing an app in Rails 2 using DataMapper as ORM. It works fine
but an unexpected downside is that generated RESTful routes does not
work. In Rails 2 you can for example write:

edit_product_path(product)

and it will use the id attribute of product to generate the URL. This
no longer works because I assume that it relies on some ActiveRecord
feature that DataMapper does not suppy. It can be solved by writing:

edit_product_path(product.id)

which is simple enough but it also applies to redirect_to for which
the solution is a bit more elaborate. Besides having to change a lot
of code in the resource scaffolds I really like the compact way of
handling routes automatically, so my question is this:

What part of Rails is responsible for making the routes work and can
it be extended in DataMapper in some way?

Kindest regards

Erik Lindblad