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I've spent whole days with PHP's DOM functions but i can't understand how it works yet. :( I have a simple XML file that looks okay but i cannot use it how i think when i've created it's structure.

Sample XML fragment:

-pages //root element
    -page id="1" //we can have any number of pages
        -product id="364826" //we can have any number of products

My original idea was to speed up my client's workflow so i throw out old CSVs and started using XMLs.

Problem 1: When i grouping products into page i'm using setIdAttribute to prevent storing the same page in the tree more than once. This works fine until reading happens because these id's are tied to some kind of DTD's (based on getElementById).

Question 1: How can i write a simple DTD which provides these necessary informations so i can use getElementById at the reading phase too?

Problem 2: Because i have pages i'd like to load as less information as i can. That was why i created the id attribute on pages. Now i cannot access my page id="2" directly because Problem 1 above (getElementById makes no sense currently). Somehow i can managed to retrieve the necessary informations about each product on a given page but my code looks scary:

$doc      = DOMDocument::load('data.xml');
$xpath    = new DOMXPath($doc);
$query    = '/pages/page[' . $page . ']'; //$page is fine: was set earlier
$products = $xpath->query($query);
$_prods   = $doc->getElementsByTagName('product');
foreach($_prods as $product){
    foreach($product->childNodes as $node){
        echo $node->nodeName . ": " . $node->nodeValue . "<br />";

Queston 2: I think the code above is the example about how not to parse an XML. But because of my limited knowledge of PHP's DOM functions i cannot write a cleaner one by myself. I tried some trivial solution but none of them worked for me.



Solving Problem 1:

The W3C defines: the meaning of the attribute xml:id as an ID attribute in XML documents and defines processing of this attribute to identify IDs in the absence of validation, without fetching external resources, and without relying on an internal subset.

In other words, when you use

$element->setAttribute('xml:id', 'test');

you do not need to call setIdAttribute, nor specify a DTD or Schema. DOM will recognize the xml:id attribute when used with getElementById without you having to validate the document or anything. This is the least effort approach. Note though, that depending on your OS and version of libxml, you wont get getElementById to work at all.

Solving Problem2:

Even with IDs not being fetchable with getElementById, you can still very much fetch them with XPath:


would definitely work. And you can also fetch the product children for a specific page directly:


Apart from this, there is very little you can do to make DOM code look less verbose, because it really is a verbose interface. It has to be, because DOM is a language agnostic interface, again defined by the W3C.

EDIT after comment below

It is working like I explained above. Here is a full test case for you. The first part is for writing new XML files with DOM. That is where you need to set the xml:id attribute. You use this instead of the regular, non-namespaced, id attribute.

// Setup
$dom = new DOMDocument;
$dom->formatOutput = TRUE;
$dom->preserveWhiteSpace = FALSE;

// How to set a valid id attribute when not using a DTD or Schema
$page1 = $dom->createElement('page');
$page1->setAttribute('xml:id', 'p1');
$page1->appendChild($dom->createElement('product', 'foo1'));
$page1->appendChild($dom->createElement('product', 'foo2'));

// How to set an ID attribute that requires a DTD or Schema when reloaded
$page2 = $dom->createElement('page');
$page2->setAttribute('id', 'p2');
$page2->setIdAttribute('id', TRUE);
$page2->appendChild($dom->createElement('product', 'bar1'));
$page2->appendChild($dom->createElement('product', 'bar2'));

// Appending pages and saving XML
$xml = $dom->saveXML();
unset($dom, $page1, $page2);
echo $xml;

This will create an XML file like this:

<?xml version="1.0"?>
  <page xml:id="p1">
  <page id="p2">

When you read in the XML again, the new DOM instance no longer knows you have declared the non-namespaced id attribute as ID attribute with setIdAttribute. It will still be in the XML, but id attribute will just be a regular attribute. You have to be aware that ID attributes are special in XML.

// Load the XML we created above
$dom = new DOMDocument;

Now for some tests:

foreach( $dom->getElementById('p1')->childNodes as $product) {
    echo $product->nodeValue; // Will output foo1 and foo2 with whitespace

The above works, because a DOM compliant parser has to recognize xml:id is an ID attribute, regardless of any DTD or Schema. This is explained in the specs linked above. The reason it outputs whitespace is because due to the formatted output there is DOMText nodes between the opening tag, the two product tags and the closing tags, so we are iterating over five nodes. The node concept is crucial to understand when working with XML.

foreach( $dom->getElementById('p2')->childNodes as $product) {
    echo $product->nodeValue; // Will output a NOTICE and a WARNING

The above will not work, because id is not an ID attribute. For the DOM parser to recognize it as such, you need a DTD or Schema and the XML must be validated against it.

$xPath = new DOMXPath($dom);
$page2 = $xPath->query('/pages/page[@id="p2"]')->item(0);
foreach( $page2->childNodes as $product) {
    echo $product->nodeValue; // Will output bar1 and bar2

XPath on the other hand is literal about the attributes, which means you can query the DOM for the page element with attribute id if getElementById is not available. Note that to query the page with ID p1, you'd have to include the namespace, e.g. @xml:id="p1".

$xPath = new DOMXPath($dom);
foreach( $xPath->query('/pages/page[@id="p2"]/product') as $product ) {
    echo $product->nodeValue; // Will output bar1 and bar2 wout whitespace

And like said, you can also use XPath to query anything else in the document. This one will not output whitespace, because it will only return the product elements below the page with id p2.

You can also traverse the entire DOM from a node. It's a tree structure. Since DOMNode is the most important class in DOM, you want to familiarize yourself with it.

$product = $dom->getElementsByTagName('product')->item(2);
echo $product->tagName; // 'product'
echo $dom->saveXML($product); // '<product>bar1</product>'

// Going from bar1 to foo1
$product = $product->parentNode // Page Node
                   ->parentNode // Pages Node
                   ->childNodes->item(1)  // Page p1
                   ->childNodes->item(1); // 1st Product

echo $product->nodeValue; // 'foo1'

// from foo1 to foo2 it is two(!) nodes because the XML is formatted
echo $product->nextSibling->nodeName; // '#text' with whitespace and linebreak
echo $product->nextSibling->nextSibling->nodeName; // 'product'
echo $product->nextSibling->nextSibling->nodeValue; // 'foo2'

On a sidenote, yes, I do have a typo in the original code above. It's product not products. But I find it hardly justified to claim the code does not work when all you have to change is an s. That just feels too much like wanting to be spoonfed.

Wednesday, December 7, 2022

Why don't you use DOMDocument::getElementsByTagName?

//get the number of product items
echo $doc->getElementsByTagName('productitem')->length;
 //traverse the collection of productitem
foreach($doc->getElementsByTagName('productitem') as $element){
  //$element is a DOMElement
  $nodeNames = $element->nodeName;
  echo ''.$name.':'.$value.'<br>';

As you want to traverse your document, use XPath is just greedy. Moreover you will instantiate each node of the document even if you only want one or two.

You can use hasChildNodes methode and childNodes attribute to traverse your document

function searchInNode(DOMNode $node){

     if(isGoodNode($node)){//if your node is good according to your database
         foreach($node->childNodes as $nodes){
Saturday, December 10, 2022

The poorly documented fact in play here is that when you select a namespace with ->children, it remains in effect for descendent nodes.

So when you ask for $sxe->children("soapenv", true)->Body->requestContactResponse, SimpleXML assumes you are still talking about the "soapenv" namespace, so is looking for the element <soapenv:requestContactResponse>, which doesn't exist.

To switch back to the default namespace, you need to call ->children again, with a NULL namespace:

$sx->children("soapenv", true)->Body->children(NULL)->requestContactResponse->requestContactReturn->id
Tuesday, December 20, 2022

The approach I took was to replace any entities with a unique marker that is treated as plain text by Xerces. Once converted into a Document object, the markers are replaced with Entity Reference objects.

See the convertStringToDocument() function in

Monday, December 5, 2022

When &#xe7; is "รง", then your encoding is Windows-1252 (or maybe ISO-8859-1), but not UTF-8.

Wednesday, September 21, 2022
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