/**
  * Retrieve object using using composite pkey values.
  * @param   string $product_id
  * @param   string $plugin_id
  * @param      PropelPDO $con
  * @return   ProductPlugin
  */
 public static function retrieveByPK($product_id, $plugin_id, PropelPDO $con = null)
 {
     $_instancePoolKey = serialize(array((string) $product_id, (string) $plugin_id));
     if (null !== ($obj = ProductPluginPeer::getInstanceFromPool($_instancePoolKey))) {
         return $obj;
     }
     if ($con === null) {
         $con = Propel::getConnection(ProductPluginPeer::DATABASE_NAME, Propel::CONNECTION_READ);
     }
     $criteria = new Criteria(ProductPluginPeer::DATABASE_NAME);
     $criteria->add(ProductPluginPeer::PRODUCT_ID, $product_id);
     $criteria->add(ProductPluginPeer::PLUGIN_ID, $plugin_id);
     $v = ProductPluginPeer::doSelect($criteria, $con);
     return !empty($v) ? $v[0] : null;
 }