Notifications once product quantity reaches 0

Question

I'm trying to send a notification when the product becomes out of stock. This is the code I have on my Observer:

public function detectProductChanges($observer)
{
    $product = $observer->getEvent()->getProduct();

    if ($product->hasDataChanges()) {

        try {
            $oldStock = $product->getStockItem()->getOrigData('qty');
            $newStock = $product->getStockItem()->getData('qty');

            if ($newStock != '0' || $oldStock == $newStock) {
                return $this;
            }

            // send email...

        } catch (Exception $e) {
            Mage::log($e->getTraceAsString(), null, 'my_cute.log');
        }
    }

    return $this;
}

On the config.xml file I got the following:

<!-- ... -->
  <global>
    <events>
      <catalog_product_save_after>
        <observers>
          <reports_detect_product_changes>
            <type>singleton</type>
            <class>reports/observer</class>
            <method>detectProductChanges</method>
          </reports_detect_product_changes>
        </observers>
      </catalog_product_save_after>
    </events>
  </global>
<!-- ... -->

The thing is, if I edit a product on the admin side, everything's fine, but if I proceed to checkout a product, this event is not called, can you help please?

Answer 1

You also need to observe the event checkout_submit_all_after. That one is dispatched when an order is placed. You should get as parameter the order placed and you can access the products ordered and check their qty changes.