PHP DOMElement::getElementsByTagName - Anyway to get just the immediate matching children?

Question

is there a way to retrieve only the immediate children found by a call to DOMElement::getElementsByTagName? For example, I have an XML document that has a category element.

Answer 1

Something like this should do

/**
 * Traverse an elements children and collect those nodes that
 * have the tagname specified in $tagName. Non-recursive
 *
 * @param DOMElement $element
 * @param string $tagName
 * @return array
 */
function getImmediateChildrenByTagName(DOMElement $element, $tagName)
{
    $result = array();
    foreach($element->childNodes as $child)
    {
        if($child instanceof DOMElement && $child->tagName == $tagName)
        {
            $result[] = $child;
        }
    }
    return $result;
}

edit: added instanceof DOMElement check

Answer 2

I'm afraid not. You'll have to iterate through the children or use XPath.

for ($n = $parent->firstChild; $n !== null; $n = $n->nextSibling) {
    if ($n instanceof DOMElement && $n->tagName == "xxx") {
        //...
    }
}

Example with XPath and your XML file:

$xml = ...;
$d = new DOMDocument();
$d->loadXML($xml);
$cat = $d->getElementsByTagName("subCategory")->item(0);
$xp = new DOMXpath($d);
$q = $xp->query("id", $cat); //note the second argument
echo $q->item(0)->textContent;

gives 2.

Answer 3

I don't use PHP, but if PHP actually implements the DOM API as specified the W3C, there is required to be a childNodes property on any Node object. You should be able to iterate over all of the direct children and test their tag name to see if they're the one you're looking for. Depending on what your tree looks like, this may be slower than getting all the elements by tag name and testing their tree position, or it may be significantly faster.

Answer 4

You can compare elements using ===. This will avoid instantiating a Xpath object.

$dom = new DOMDocument();
$dom->loadXML($xmlString);

$return          = array();

//find your top level element
$topLevelElement = $dom->getElementsByTagName('category');
//find all `id` child elements recursively
$idElements      = $topLevelElement->getElementsByTagName('id');

if ($idElements->length > 0) {
    foreach ($idElements as $idElement) {
        if ($idElement->parentNode === $topLevelElement) {
            $return[]   = $idElement;
       }
    }
}

//$return now holds non nested child elements

Depending on the size of your XML document you might find Xpath performs better. However in terms of elegance this solution is cleaner.