Return child nodes using xpath query

Question

I'm trying to return all the "field" children of the node "core" below:

<archive xmlns="http://rs.tdwg.org/dwc/text/" metadata="eml.xml">
  <core encoding="utf-8" fieldsTerminatedBy="\t" linesTerminatedBy="\n" fieldsEnclosedBy="" ignoreHeaderLines="1" rowType="http://rs.tdwg.org/dwc/terms/Occurrence">
    <files>
      <location>occurrence.txt</location>
    </files>
    <id index="0" />
    <field index="1" term="http://rs.tdwg.org/dwc/terms/class"/>
    <field index="2" term="http://rs.tdwg.org/dwc/terms/maximumDepthInMeters"/>
    <field index="3" term="http://purl.org/dc/terms/language"/>
    <field index="4" term="http://rs.tdwg.org/dwc/terms/coordinatePrecision"/>
    <field index="5" term="http://rs.tdwg.org/dwc/terms/decimalLatitude"/>
 </core>
</archive

I have the following PHP:

$xml = new \DOMDocument();
$xml->preserveWhiteSpace = false;
$xml->load($input_xml);

$xpath = new \DOMXpath($xml);
$xpath->registerNamespace('ns', $xml->documentElement->namespaceURI);

Something like this works for retrieving a specific "field" and getting it's index:

$query = $xpath->query("//ns:field[contains(@term, 'http://rs.tdwg.org/dwc/terms/class')]")->item(0);
$url = $query->attributes->getNamedItem("index")->nodeValue;

I've tried queries like the following using all sorts of examples on the net. None of them worked:

$children = $xpath->query("//ns:core/field");
$children = $xpath->query("//core/field");
$children = $xpath->query("/core/field");
$children = $xpath->query("/core/*");
$children = $xpath->query("/archive/core/field");
$children = $xpath->query("//ns:core/ns:field");

Ultimately, what I'm trying to achieve is returning all "field" nodes under "core", loop through them, and create an array from their index and term. For example:

$myArray = array(
    "1" => "http://rs.tdwg.org/dwc/terms/class",
    "2" => "http://rs.tdwg.org/dwc/terms/maximumDepthInMeters",
    "3" => "http://purl.org/dc/terms/language",
);

Any help would be appreciated. Thanks.

Answer 1

It might be the namespace that was tripping you up; you were also not querying the correct attribute (you were looking at index , but the URLs are in term ). Try this code:

foreach( $xpath->query('/ns:archive/ns:core/ns:field') as $field) {
    if ( $field->attributes->getNamedItem("term")->nodeValue ) {
        echo "URL: " . $field->attributes->getNamedItem("term")->nodeValue . "\n";
    }
}