如何使用学说在单个查询中获取整个树?

This snippet from official website works as expected:

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

foreach ($treeObject->fetchRoots() as $root) {
  $options = array(
      'root_id' => $root->$rootColumnName
  );
  foreach($treeObject->fetchTree($options) as $node) {
    echo str_repeat(' ', $node['level']) . $node['name'] . "
";
  }
}

但我看到有几十个查询发送到数据库.

Doctrine_Core::getTable('YourTableWithTree')->createQuery('tree')
    ->addOrderBy('tree.root_id ASC')
    ->addOrderBy('tree.lft ASC');