Integrity constraint violation in Magento custom module - sql

Question

I have a similar probelm to Integrity constraint violation creating Product in Magento (unanswered) but I am creating a custom Observer that hooks into the catalog_product_save_after event - based on this tutorial: http://fishpig.co.uk/blog/custom-tabs-magento-product-admin.html
However whenever a new product is saved I get this error:
SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '22-1' for key 'UNQ_CATALOGINVENTORY_STOCK_ITEM_PRODUCT_ID_STOCK_ID'
The config.xml looks like this:
<adminhtml>
<events>
<catalog_product_save_after>
<observers>
<a1web_save_product_data>
<type>singleton</type>
<class>metricimperial/observer</class>
<method>saveProductData</method>
</a1web_save_product_data>
</observers>
</catalog_product_save_after>
</events>
</adminhtml>
The outline of the class is like this:
<?php
class A1web_MetricImperialConverter_Model_Observer
{
/**
* Flag to stop observer executing more than once
*
* #var static bool
*/
static protected $_singletonFlag = false;
* #param Varien_Event_Observer $observer
*/
public function saveProductData(Varien_Event_Observer $observer)
{
if (!self::$_singletonFlag) {
self::$_singletonFlag = true;
$product = $observer->getEvent()->getProduct();
//Custom updates made to product object here
$product->save();
}
catch (Exception $e) {
Mage::getSingleton('adminhtml/session')->addError($e->getMessage());
}
}
}
/**
* Retrieve the product model
*
* #return Mage_Catalog_Model_Product $product
*/
public function getProduct()
{
return Mage::registry('product');
}
/**
* Shortcut to getRequest
*
*/
protected function _getRequest()
{
return Mage::app()->getRequest();
}
}
The product is saved correctly with the custom product data I'm adding - and once the product is saved the error does not occur on subsequent saves of the same product. It is just when the product is first created the error occurs.
Thanks in advance

Answer 1

Instead of using $product->save() try using the resource model, a la $product->getResource()->save($product).
The reason being $product->save() will re-trigger all save events, hence running whatever is saving the cataloginventory_stock and throwing the error.

Answer 2

In this case, I'd recommend not using the catalog_product_save_after event. Instead, try using catalog_product_prepare_save which is fired after the POST data is applied to the product, but before ->save() is called. That way you don't have to mess with with saving or that ugly $_singletonFlag!
Also, with catalog_product_prepare_save you get the HTTP Request object inside the Observer Event. No need for Mage::app()->getRequest(). Woot!