Question regarding the creation of an credit_card object on Ryan bates Active_Merchant intergration video

I was going through Ryan Bates' video on Active Merchant integration video Railscast #145 and my question was regarding the creation of the @credit_card method that he defines within the Order.rb method.

def credit_card
  @credit_card||=ActiveMerchant::Billing::CreditCard.new(
    :type=>card_type,
    :number=>card_number,
    :verification_value=>card_verification,
    :month=>ca开发者_C百科rd_expires_on.month,
    :year=>card_expires_on.year,
    :first_name=>first_name,
    :last_name=>last_name
  )

end

What I don't follow is how does this method get called. The form_for in the new method creates an @order object while and there is no mention of the credit_card method. How does the credit_card method get called to initiate the creation of the @credit_card object.

I am aware of virtual attributes but I dont know how the credit_card method is actually called.

---

Looking at the screencast code here.

In app/views/orders/new.html.erb

We can see the order form, and from the first line

<% form_for @order do |f| %>

We see that, on submission, the form use the oders_controller create method.

In app/controller/orders_controller.rb

    def create
      @order = current_cart.build_order(params[:order])
      @order.ip_address = request.remote_ip

      if @order.save
        if @order.purchase
          render :action => "success"
        else
          render :action => "failure"
        end
      else
        render :action => 'new'
      end
    end

We can see that @order is Order instance built from the cart. Nothing special here This order is now saved with @order.save and then the purchase method is called on @order

Let's take a look at this purchase method!

in app/model/order.rb

    def purchase
      response = GATEWAY.purchase(price_in_cents, credit_card, purchase_options)
      transactions.create!(:action => "purchase", :amount => price_in_cents, :response => response)
      cart.update_attribute(:purchased_at, Time.now) if response.success?
      response.success?
    end

Second line response = GATEWAY.purchase(price_in_cents, credit_card, purchase_options) . The credit_card method is called there as an argument of GATEWAY.purchase