script/generate nifty_scaffold payment_notification params:text cart_id:integer status:string transaction_id:string create
rake db:migrate
curl -d "txn_id=3XC103945N720211C&invoice=923204115&payment_status=Completed" http://localhost:3000/payment_notifications



# payment_notifications_controller.rb
protect_from_forgery :except => [:create]

def create
  PaymentNotification.create!(:params => params, :cart_id => params[:invoice], :status => params[:payment_status], :transaction_id => params[:txn_id])
  render :nothing => true
end

# models/payment_notification.rb
belongs_to :cart
serialize :params
after_create :mark_cart_as_purchased

private

def mark_cart_as_purchased
  if status == "Completed"
    cart.update_attribute(:purchased_at, Time.now)
  end
end

# controllers/application.rb
def current_cart
  if session[:cart_id]
    @current_cart ||= Cart.find(session[:cart_id])
    session[:cart_id] = nil if @current_cart.purchased_at
  end
  if session[:cart_id].nil?
    @current_cart = Cart.create!
    session[:cart_id] = @current_cart.id
  end
  @current_cart
end

# models/cart.rb
def paypal_url(return_url, notify_url)
  values = {
    :business => 'seller_1229899173_biz@railscasts.com',
    :cmd => '_cart',
    :upload => 1,
    :return => return_url,
    :invoice => id,
    :notify_url => notify_url
  }
  line_items.each_with_index do |item, index|
    values.merge!({
      "amount_#{index+1}" => item.unit_price,
      "item_name_#{index+1}" => item.product.name,
      "item_number_#{index+1}" => item.id,
      "quantity_#{index+1}" => item.quantity
    })
  end
  "https://www.sandbox.paypal.com/cgi-bin/webscr?" + values.to_query
end



<!-- carts/show.html.erb -->
<%= link_to "Checkout", @cart.paypal_url(products_url, payment_notifications_url) %>