使用默认命名空间绑定的XML上的XML xpath查询

下面是一个示例XML文件和一个PHP CLI脚本,它执行作为参数给出的xpath查询.对于此测试用例,命令行是：

./xpeg "//MainType[@ID=123]"

最奇怪的是这条线,没有它我的方法不起作用：

$result->loadXML($result->saveXML($result));

据我所知,这只是重新解析修改后的XML,在我看来这不应该是必要的.

有没有更好的方法在PHP中对此XML执行xpath查询？

XML(注意默认命名空间的绑定)：

<?xml version="1.0" encoding="utf-8"?>
<MyRoot
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://www.example.com/data http://www.example.com/data/MyRoot.xsd"
 xmlns="http://www.example.com/data">
  <MainType ID="192" comment="Bob's site">
    <Price>$0.20</Price>
    <TheUrl><![CDATA[http://www.example.com/path1/]]></TheUrl>
    <Validated>N</Validated>
  </MainType>
  <MainType ID="123" comment="Test site">
    <Price>$99.95</Price>
    <TheUrl><![CDATA[http://www.example.com/path2]]></TheUrl>
    <Validated>N</Validated>
  </MainType>
  <MainType ID="922" comment="Health Insurance">
    <Price>$600.00</Price>
    <TheUrl><![CDATA[http://www.example.com/eg/xyz.php]]></TheUrl>
    <Validated>N</Validated>
  </MainType>
  <MainType ID="389" comment="Used Cars">
    <Price>$5000.00</Price>
    <TheUrl><![CDATA[http://www.example.com/tata.php]]></TheUrl>
    <Validated>N</Validated>
  </MainType>
</MyRoot>

PHP CLI脚本：

#!/usr/bin/php-cli
<?php

$xml = file_get_contents("xpeg.xml");

$domdoc = new DOMDocument();
$domdoc->loadXML($xml);

// remove the default namespace binding
$e = $domdoc->documentElement;
$e->removeAttributeNS($e->getAttributeNode("xmlns")->nodeValue,"");

// hack hack,cough cough,hack hack
$domdoc->loadXML($domdoc->saveXML($domdoc));

$xpath = new DOMXpath($domdoc);

$str = trim($argv[1]);
$result = $xpath->query($str);
if ($result !== FALSE) {
  dump_dom_levels($result);
}
else {
  echo "errorn";
}

// The following function isn't really part of the
// question. It simply provides a concise summary of
// the result.
function dump_dom_levels($node,$level = 0) {
  $class = get_class($node);
  if ($class == "DOMNodeList") {
    echo "Level $level ($class): $node->length itemsn";
    foreach ($node as $child_node) {
      dump_dom_levels($child_node,$level+1);
    }
  }
  else {
    $nChildren = 0;
    foreach ($node->childNodes as $child_node) {
      if ($child_node->hasChildNodes()) {
        $nChildren++;
      }
    }
    if ($nChildren) {
      echo "Level $level ($class): $nChildren childrenn";
    }
    foreach ($node->childNodes as $child_node) {
      if ($child_node->hasChildNodes()) {
        dump_dom_levels($child_node,$level+1);
      }
    }
  }
}
?>