gistfile1.rb

# Routes
# To prevent too deep nesting, we make the show, edit, update and destroy actions not nested under the category. We have a lot of models nested inside the product.

resources :category do
  resources :products, :only => [:new, :create, :index]
end
resources :products, :only => [:show, :edit, :update, :destroy]

# ProductController
# We need to expose :category, :products and :product

class ProductController < ApplicationController

  expose(:category) {
    if params[:category_id].present?
      Category.find(params[:category_id])
    else
      product.category
    end
  } # to support the half-nested half-unnested Routes setup above we have to fetch the category depending on the url-param
  expose(:products) { category.products } # for the #index action
  expose(:product)
end