Magento Record Amount of Money Used on Coupon Code - magento

Question

I am well aware of finding out the number of times a coupon code was used (salesrule/coupon model). However, I would like to know how to intercept the use of a coupon and record its grand total in a table.
I have tried to do this by overriding the successAction() method of the Mage_Checkout_OnepageController, however if I try to get the coupon code with
$couponCode = (string) Mage::getSingleton('checkout/cart')->getQuote()->getCouponCode();
$couponCode turns out to be a blank string. It would seem that, by the time the successAction is called, the checkout/cart singleton has already been emptied. How can I intercept the 'place order' button and still be able to get the coupon code the customer used?
All help is greatly appreciated and I always accept an answer!

Answer 1

Upon entry of the successAction the _quote property of the checkout/cart object is already nullified.
However, you still can get your data upon entry of the successAction by using:
$oOrder = Mage::getModel('sales/order')
->load($this->getOnePage()->getCheckout()->getLastOrderId());
var_dump(
$oOrder->getCouponCode(),
$oOrder->getDiscountAmount(),
$oOrder->getGrandTotal()
);
But I'd recommend to create an observer for the checkout_onepage_controller_success_action event instead. This way you don't have to override anything at all. And usually nothing to maintain when it comes to Magento upgrades.
The code of such observer would look similiar like this:
/**
* checkout_onepage_controller_success_action event observer
*
* #param object $oObserver
* #return null
*/
public function checkoutOnepageControllerSuccessAction($oObserver)
{
$aOrderId = $oObserver->getOrderIds();
foreach ($aOrder as $iOrderId) {
$oOrder = Mage::getModel('sales/order')->load($iOrderId);
var_dump(
$oOrder->getCouponCode(),
$oOrder->getDiscountAmount(),
$oOrder->getGrandTotal()
);
}
}