public function updateSubtreeModificationTime($pathString, $timestamp = null)
{
$nodes = array_filter(explode('/', $pathString));
$query = $this->handler->createUpdateQuery();
$query->update($this->handler->quoteTable('ezcontentobject_tree'))->set($this->handler->quoteColumn('modified_subnode'), $query->bindValue($timestamp ?: time()))->where($query->expr->in($this->handler->quoteColumn('node_id'), $nodes));
$query->prepare()->execute();
}