Selecting parent nodes with XMLReader

Question

I had to rewrite part of a programme to use XMLReader to select parts of an XML file for processing.

Take this simplified XML as an example:

Answer 1

XMLReader can expand() the current node into a DOMNode. This will load only the node and its descendants into memory.

After that, you can use a DOMXPath instance or convert the node into a SimpleXMLElement.

$reader = new XMLReader();
$reader->open('data:/text/xml,'.urlencode($xml));

$dom = new DOMDocument();
$xpath = new DOMXpath($dom);

while($reader->read()) {
  if (
    $reader->nodeType == XMLReader::ELEMENT && 
    $reader->localName == 'bet'
  ) {
    $bet= $reader->expand($dom);
    if ($xpath->evaluate('count(selection[@selectionid = "52411062.1"]) > 0', $bet)) {
      var_dump($dom->saveXml($bet));
    }
  }
}

You will always have to decide which part to implement in XMLReader and which in DOM/SimpleXML. In XMLReader you will have to validate the nodes and maintain a state, but can avoid to load the data. At one point in the parsing the XML snippets will be small enough and you can use expand().