Retrieving a subset of XML nodes with PHP

Question

Using PHP, how do I get an entire subset of nodes from an XML document? I can retrieve something like:

Answer 1

Use DOM and XPath. Xpath allows you to select nodes (and values) from an XML DOM.

$dom = new DOMDocument();
$dom->loadXml($xml);
$xpath = new DOMXpath($dom);

$result = '';
foreach ($xpath->evaluate('/people/certain') as $node) {
  $result .= $dom->saveXml($node);
}

echo $result;

Demo: https://eval.in/162149

DOMDocument::saveXml() has a context argument. If provided it saves that node as XML. Much like outerXml(). PHP is able to register your own classes for the DOM nodes, too. So it is even possible to add an outerXML() function to element nodes.

class MyDomElement extends DOMElement {
  public function outerXml() {
    return $this->ownerDocument->saveXml($this);
  }
}

class MyDomDocument extends DOMDocument {
  public function __construct($version = '1.0', $encoding = 'utf-8') {
    parent::__construct($version, $encoding);
    $this->registerNodeClass('DOMElement', 'MyDomElement');
  }
}

$dom = new MyDomDocument();
$dom->loadXml($xml);
$xpath = new DOMXpath($dom);

$result = '';
foreach ($xpath->evaluate('/people/certain') as $node) {
  $result .= $node->outerXml();
}

echo $result;

Demo: https://eval.in/162157