Get ancestor node with PHP and xpath

Question

Please forgive if the following is a bit muddled, I've been killing myself trying to work this out.

This is a chunk of XML (exported from a much large site) that I am using to create a category tree for a mini-CMS. Once I've got the value and name of the node, which is no problem, I also need to get the 'parent' each node, that is, the node preceding it which is above it in the hierarchy.

    <productCategory>
    <genericName>DigitalCinema</genericName>
    <productCategories>
      <productCategory>
        <genericName>DCinemaProj</genericName>
        <productModels>
          <productModel>ProjProd-1</productModel>
          <productModel>ProjProd-2</productModel>
          <productModel>ProjProd-3</productModel>
          <productModel>ProjProd-4</productModel>
        </productModels>
      </productCategory>
      <productCategory>
        <genericName>DCinemaLens</genericName>
      </productCategory>
    </productCategories>
  </productCategory>

For example, for the productCategory-genericName DCinemaLens, I need to be able to grab the parent as DigitalCinema, and similarly for the individual productModel nodes, where the parent would be DCinemaProj.

I've tried various different queries in xpath using ancestor, previous-sibling and parent and I still can't see to grab the node I need.

Here is my code as it stands from giving up on my attempts a few minutes ago.

if ($xml->xpath('//productCategories')) {

    foreach($xml->xpath('//genericName | //productModel') as $genericName){

    echo "<p align='center'>$genericName";

    $type = $genericName->getName();

    echo " - (" . $type . ") ";

    $derp = $xml->xpath("ancestor::productCategory[1]/genericName");

    echo $derp;

    echo '</p>';

    }

    }

I've also had some success getting information in an array, but it always just returns every value in the XML again.

$key = 'genericName';

    $derpgleep = $derp[$key];

    echo 'Derp= ' . $derpgleep;

    print_r($derp);

Hopefully there is a really easy solution I am overlooking. I hope I have been clear.

Good question, +1. See my answer for a complete, short and simple XPath expression that selects the wanted, called "parent", node. — Dimitre Novatchev

Emiliano Poggi Emiliano Poggi · Accepted Answer · 2011-09-05T18:09:11

The XPath expression you are using:

 ancestor::productCategory[1]/genericName

would work if you were able to perform that expression starting from the current node. this is not possible indeed starting from the current Array $genericName as it does not contain parents, nor ancestors.

I think that your option is to re-traverse all the XML tree. This is a sample test which works as required, based on your input sample.

<?php
$xml = simplexml_load_file("test_input1.xml");

if ($xml->xpath('//productCategories')) {

    foreach($xml->xpath('//genericName') as $genericName){

        echo "<p align='center'>$genericName";

        $type = $genericName->getName();

        echo " - (" . $type . ") ";

        $derp = $xml->xpath("//genericName[.='" . 
            $genericName[0] . 
            "']/ancestor::productCategory[2]/genericName");

        echo $derp[0];  echo "</p>\n";
    }
}
?>

This will print out the following HTML fragment:

<p align='center'>DigitalCinema - (genericName) </p>
<p align='center'>DCinemaProj - (genericName) DigitalCinema</p>
<p align='center'>DCinemaLens - (genericName) DigitalCinema</p>

While to get the "parent" of productModel you need an xpath like:

        $derp = $xml->xpath("//productModel[.='" . 
            $productModel[0] . 
            "']/parent::productCategory[1]/genericName");

Get ancestor node with PHP and xpath

2 Answers