Ruby On Rails 2nd Edition Error Report

1. NoMethodError in StoreController#add_to_cart
undefined method `product' for #<Product:0x4a02900>

Reason :
Session Problem

Solution:
clean the session and retart the server
rake db:sessions:clear


2. Cart.Item nil.object found when use the redirect_to_index

reason:
Session not loaded by the redirect.

Solution:
def index
   @products = Product.find_products_for_sale
   @cart = find_cart
end

3. Submit Button doesn't display when trail on the AJax sample

Reason:
version problem, and the tag name is not correct

Solution:
<%= form_remote_tag :url => { :action => :add_to_cart, :id => product } %>
   <%= submit_tag "Add to Cart" %>
<%= end_form_tag %>