Rails - Mar 2005 - Using a params from down the model relationship tree

Hi,

I have three models:

class Product < ActiveRecord::Base
	has_many :parts
end

class Part < ActiveRecord::Base
	has_many :part_applications
	belongs_to :product
end

class PartApplication < ActiveRecord::Base
	belongs_to :part
end


In a controller, I have access to a Product.id:

@product = Product.find(@params[''id''])

So with that I am able to do something like this:

@product.parts.each do |part|
  part.part_applications.each do |app|
  end
end

But what I would like to be able to do is start iterating at the other
end, but based on the Product.id found in @params[''id'']:

@part_applications.each do |app|
end

Is there a way to be able to do this without having to use find_by_sql?