After introducting the CartItem object, the app blows up with :
NoMethodError in StoreController#add_to_cart
undefined method `product' for #<Product:0x2498b0c>
RAILS_ROOT: script/../config/.. Application Trace | Framework Trace | Full Trace
vendor/rails/activerecord/lib/active_record/base.rb:1850:in `method_missing' app/models/cart.rb:9:in `add_product' app/controllers/store_controller.rb:11:in `add_to_cart'
This happens even after clearning sessions using rake. When I use a different browser (Safari), it works. Looks like the session was getting cached by Firefox. Hope this helps someone.