Doctrine 如何获取嵌套集合中节点的父id

我有以下代码：

$treeObject = Doctrine_Core::getTable('Category')->getTree();
$rootColumnName = $treeObject->getAttribute('rootColumnName');

foreach ($treeObject->fetchRoots() as $root) {
  $options = array( 'root_id' => $root->$rootColumnName  );

  foreach($treeObject->fetchTree($options) as $node) {
    $parent_id = $node->getNode()->getParent()->getId();
    echo $parent_id;
  }
}

这很好，但是getparent（）调用会对每个节点执行查询。可以在不运行数百个额外查询的情况下检索父id