PHP DOM: How to get child elements by tag name in an elegant manner?

Question

I'm parsing some XML with PHP DOM extension in order to store the data in some other form. Quite unsurprisingly, when I parse an element I pretty often need to obtain all children elements of some name. There is the method DOMElement::getElementsByTagName($name) , but it returns all descendants with that name, not just immediate children. There is also the property DOMNode::$childNodes but (1) it contains node list, not element list, and even if I managed to turn the list items into elements (2) I'd still need to check all of them for the name. Is there really no elegant solution to get only the children of some specific name or am I missing something in the documentation?

Some illustration:

<?php

DOMDocument();
$document->loadXML(<<<EndOfXML
<a>
  <b>1</b>
  <b>2</b>
  <c>
    <b>3</b>
    <b>4</b>
  </c>
</a>
EndOfXML
);

$bs = $document
    ->getElementsByTagName('a')
    ->item(0)
    ->getElementsByTagName('b');

foreach($bs as $b){
    echo $b->nodeValue . "\n";
}

// Returns:
//   1
//   2
//   3
//   4
// I'd like to obtain only:
//   1
//   2

?>

Answer 1

simple iteration process

$parent = $p->parentNode;

foreach ( $parent->childNodes as $pp ) {

    if ( $pp->nodeName == 'p' ) {

        if ( strlen( $pp->nodeValue ) ) {
            echo "{$pp->nodeValue}\n";
        }

    }

}

Answer 2

An elegant manner I can imagine would be using a FilterIterator that is suitable for the job. Exemplary one that is able to work on such a said DOMNodeList and (optionally) accepting a tagname to filter for as an exemplary DOMElementFilter from the Iterator Garden does:

$a = $doc->getElementsByTagName('a')->item(0);

$bs = new DOMElementFilter($a->childNodes, 'b');

foreach($bs as $b){
    echo $b->nodeValue . "\n";
}

This will give the results you're looking for:

1
2

You can find DOMElementFilter in the Development branch now. It's perhaps worth to allow * for any tagname as it's possible with getElementsByTagName("*") as well. But that's just some commentary.

Hier is a working usage example online: https://eval.in/57170

Answer 3

My solution used in a production:

Finds a needle (node) in a haystack (DOM)

function getAttachableNodeByAttributeName(\DOMElement $parent = null, string $elementTagName = null, string $attributeName = null, string $attributeValue = null)
{
    $returnNode = null;

    $needleDOMNode = $parent->getElementsByTagName($elementTagName);

    $length = $needleDOMNode->length;
    //traverse through each existing given node object
    for ($i = $length; --$i >= 0;) {

        $needle = $needleDOMNode->item($i);

        //only one DOM node and no attributes specified?
        if (!$attributeName && !$attributeValue && 1 === $length) return $needle;
        //multiple nodes and attributes are specified
        elseif ($attributeName && $attributeValue && $needle->getAttribute($attributeName) === $attributeValue) return $needle;
    }

    return $returnNode;
}

Usage:

$countryNode = getAttachableNodeByAttributeName($countriesNode, 'country', 'iso', 'NL');

Returns DOM element from parent countries node by specified attribute iso using country ISO code 'NL', basically like a real search would do. Find a certain country by it's name in an array / object.

Another usage example:

$productNode = getAttachableNodeByAttributeName($products, 'partner-products');

Returns DOM node element containing only single (root) node, without searching by any attribute. Note: for this you must make sure that root nodes are unique by elements' tag name, eg countries->country[ISO] - countries node here is unique and parent to all child nodes.