rails 3 get data from an association and display in flash message - ruby-on-rails

Question

I'm using ActiveMerchant with Authorize.net and already setup 2 models Order and Transaction. (http://railscasts.com/episodes/145-integrating-active-merchant)
I would like to get error message from the transaction if error occurred then output in flash message. Here is my code:
#order_controller.rb
def create
#order = Order.new(params[:order])
respond_to do |format|
if #order.save
if #order.purchase
format.html { redirect_to(#order, :notice => 'Order was successfully created.') }
format.xml { render :xml => #order, :status => :created, :location => #order }
else
flash[:error] = #order.transactions.response
format.html { render :action => "new" }
end
else
format.html { render :action => "new" }
format.xml { render :xml => #order.errors, :status => :unprocessable_entity }
end
end
end
And here is my transaction model:
#models/order_transaction.rb
class OrderTransaction < ActiveRecord::Base
belongs_to :order
serialize :params
def response=(response)
self.success = response.success?
self.authorization = response.authorization
self.message = response.message
self.params = response.params
rescue ActiveMerchant::ActiveMerchantError => e
self.success = false
self.authorization = nil
self.message = e.message
self.params = {}
end
end
The transaction data has been saved to the database as below:
#models/order.rb
class Order < ActiveRecord::Base
has_many :transactions, :class_name => "OrderTransaction"
attr_accessor :card_type, :card_number, :card_month, :card_year, :card_verification
def purchase
response = GATEWAY.purchase(charge_amount, credit_card, purchase_options)
transactions.create!(:action => "purchase", :amount => charge_amount, :response => response)
response.success?
end
...
end
I want to flash up this transaction error message when transaction failed. And what would I should do to get these errors if I have 2 transactions for one order.?
Any help would be much appreciated.
Thanks!