static function getParent($id)
 {
     if (!Validator::number($id, 1)) {
         return null;
     }
     $context = Model_Context::getInstance();
     $pool = new DBModel();
     $pool->reset('Categories');
     $blogid = intval($context->getProperty('blog.id'));
     $pool->setQualifier('blogid', 'equals', $blogid);
     $pool->setQualifier('id', 'equals', $id);
     return $pool->getCell('parent');
 }