/**
  * Collect validated attributes
  *
  * @param Mage_Catalog_Model_Resource_Eav_Mysql4_Product_Collection $productCollection
  * @return Mage_CatalogRule_Model_Rule_Condition_Product
  */
 public function collectValidatedAttributes($productCollection)
 {
     $attribute = $this->getAttribute();
     if ($attribute == 'category_ids' || $this->isFilterCustom($attribute)) {
         return $this;
     }
     if ($this->getAttributeObject()->isScopeGlobal()) {
         $attributes = $this->getRule()->getCollectedAttributes();
         $attributes[$attribute] = true;
         $this->getRule()->setCollectedAttributes($attributes);
         $productCollection->addAttributeToSelect($attribute, 'left');
     } else {
         $this->_entityAttributeValues = $productCollection->getAllAttributeValues($attribute);
     }
     return $this;
 }