/**
 * Retrieve object using using composite pkey values.
 * @param      int $category_id
   @param      int $article_id
   
 * @param      PropelPDO $con
 * @return     BlogCategoryArticle
 */
 public static function retrieveByPK($category_id, $article_id, PropelPDO $con = null)
 {
     $key = serialize(array((string) $category_id, (string) $article_id));
     if (null !== ($obj = BlogCategoryArticlePeer::getInstanceFromPool($key))) {
         return $obj;
     }
     if ($con === null) {
         $con = Propel::getConnection(BlogCategoryArticlePeer::DATABASE_NAME, Propel::CONNECTION_READ);
     }
     $criteria = new Criteria(BlogCategoryArticlePeer::DATABASE_NAME);
     $criteria->add(BlogCategoryArticlePeer::CATEGORY_ID, $category_id);
     $criteria->add(BlogCategoryArticlePeer::ARTICLE_ID, $article_id);
     $v = BlogCategoryArticlePeer::doSelect($criteria, $con);
     return !empty($v) ? $v[0] : null;
 }