Yeah, it's kind of a pain that Magento doesn't leave any history around in the order record when you use sale pricing with regard to how that base price was calculated.
Fortunately it's open source, so you can patch this in if you like.
I recently wrote an observer that fires when the order record is loaded, to address this very issue. It cross-references the line base_price with the product's current full-retail price. If there is a mismatch, it adds a couple fields to the order item to help expose this info to any external script that's listening (in our case, a custom order fulfillment script that relays orders to SAP using Magento's SOAP API).
Here's the basic idea - make a module in app/code/local/YourCo/SalePricing
and set up an observer class in app/code/local/YourCo/SalePricing/Model/Promo/Observer.php
<?php
class YourCo_SalePricing_Model_Promo_Observer
{
public function __construct()
{
}
// tag order items that have a sale-price
// with original retail price and total sale discount for this line
public function report_sale_pricing($observer)
{
$event = $observer->getEvent();
$order = $event->getOrder();
$items = $order->getAllItems();
foreach ($items as $item) {
// heads up, you may want to do this for other types as well...
if ($item->getProductType() == Mage_Catalog_Model_Product_Type::TYPE_CONFIGURABLE) {
$regular_price = $this->_lookupFullRetail($item,$order->getStoreId());
$sale_price = $item->getBasePrice();
if ($regular_price - $sale_price > 0.005) {
$qty = $item->getQtyOrdered();
$total_sale_discount = ($regular_price * $qty) - ($sale_price * $qty);
$item->setFullRetailPrice((string)$regular_price);
$item->setSaleDiscount((string)$total_sale_discount);
}
}
}
}
private function _lookupFullRetail(&$item,$store_id)
{
$mpid = $item->getProductId();
$p = Mage::getModel('catalog/product')->setStoreId($store_id)->load($mpid);
return $p->getPrice();
}
}
Your module's etc/config.xml needs to tell magento when to run your observer:
<?xml version="1.0"?>
<config>
<global>
<models>
<yourco_salepricing>
<class>YourCo_SalePricing_Model</class>
</yourco_salepricing>
</models>
<events>
<sales_order_load_after>
<observers>
<yourco_salepricing>
<type>singleton</type>
<class>YourCo_SalePricing_Model_Promo_Observer</class>
<method>report_sale_pricing</method>
</yourco_salepricing>
</observers>
</sales_order_load_after>
</events>
</global>
</config>
Make sure to activate your new module in app/etc/modules/... and clear the config cache.
Now, when you load the order, you can loop over each item and check for $item->getFullRetailPrice() -- if it's there, you know the item was on sale (well, either that or the price has gone up since the order was placed). You still don't know why, ie which sale price rule was in force, but for our application we didn't really care, and getting that info to be saved with the order would have been a much tougher mod.
