Using DOMXml and Xpath, to update XML entries

gistfile1.aw

<?php
/**
 * http://stackoverflow.com/questions/9671273/using-domxml-and-xpath-to-update-xml-entries
 */

$xml = <<<XML
<?xml version="1.0" encoding="UTF-8"?>
<storagehouse xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:noNamespaceSchemaLocation="schema.xsd">
    <item id="c7278e33ef0f4aff88da10dfeeaaae7a">
        <name>HDMI Cable 3m</name>
        <weight>0.5</weight>
        <category>Cables</category>
        <location>B3</location>
    </item>
    <item id="df799fb47bc1e13f3e1c8b04ebd16a96">
        <name>Dell U2410</name>
        <weight>2.5</weight>
        <category>Monitors</category>
        <location>C2</location>
    </item>
</storagehouse>
XML;

class ItemNode
{
    private $node;
    private $createData;

    public function __construct(DOMNode $node)
    {
        $this->node = $node;
        $this->snapshot();
    }

    /**
     * did the repository node changed since last snapshot?
     *
     * @return bool
     */
    public function hasChanged() {
        return !$this->arraysAreEqual($this->getData(), $this->createData);
    }

    /**
     * compare arrays for equality but w/o key order
     * @param array $a
     * @param array $b
     * @return bool
     */
    private function arraysAreEqual(array $a, array $b)
    {
        if (count($a) != count($b)) {
            return FALSE;
        }
        foreach($a as $name => $value)
        {
            if (!array_key_exists($name, $b)) return FALSE;
            if ($b[$name] !== $a[$name]) return FALSE;
        }
        return TRUE;
    }

    public function itemHasChanges(Item $item)
    {
        return !$this->arraysAreEqual(get_object_vars($item), $this->createData);
    }

    public function snapshot()
    {
        $this->createData = $this->getData();
    }

    public function overloadObject($object)
    {
        foreach ($this->getData() as $name => $value) {
            $object->$name = $value;
        }
    }

    /**
     * @return array
     */
    public function getData()
    {
        $values = array();
        foreach ($this->node->childNodes as $child) {
            /* @var $child DOMElement */
            if ($child instanceof DOMElement) {
                $values[$child->localName] = $child->nodeValue;
            }
        }
        return $values;
    }

    public function updateWith(Item $item)
    {
        $data = get_object_vars($item);
        $this->setData($data);
        $this->snapshot();
    }

    public function setData(array $data)
    {
        foreach ($data as $name => $value)
        {
            $this->setValue($name, $value);
        }
    }

    private function setValue($name, $value)
    {
        $xp = new DOMXPath($this->node->ownerDocument);
        $result = $xp->query(sprintf('./%s', $name), $this->node);
        if (!$result || $result->length != 1) {
            throw new InvalidArgumentException(sprintf('Value "%s" does not exist.', $name));
        }
        $result->item(0)->nodeValue = $value;
    }
}

class Repository
{
    private $doc;
    private $provided = array();

    public function __construct($xml)
    {
        $doc = new DOMDocument();
        $doc->loadXML($xml);
        $this->doc = $doc;
    }

    public function getItemByID($id)
    {
        $xp = new DOMXPath($this->doc);
        if (($result = $xp->query(sprintf('//item[@id="%s"]', $id))) && $result->length == 1) {
            $node = new ItemNode($result->item(0));
            $item = new Item($id);
            $node->overloadObject($item);
            $this->register($item, $node);
            return $item;
        } else {
            throw new InvalidArgumentException(sprintf('No Item with id "%s" exists.', $id));
        }
    }

    private function register($object, ItemNode $node)
    {
        $this->provided[] = array($object, $node);
    }

    public function saveChanges()
    {
        $updates = array();
        foreach($this->provided as $entity)
        {
            /* @var $object Item */
            /* @var $node ItemNode */
            list($object, $node) = $entity;
            if ($node->hasChanged()) {
                throw new UnexpectedValueException('Transaction not safe (DOMElement Node has changed).');
            }
            if ($node->itemHasChanges($object)) {
                $changes[] = $entity;
            }
        }
        if (!count($changes)) {
            return;
        }

        foreach($changes as $entity) {
            list($object, $node) = $entity;
            $node->updateWith($object);
        }
    }

    public function getXML() {
        return $this->doc->saveXML();
    }
}

class Item
{
    private $id;

    public function __construct($id)
    {
        $this->id = $id;
    }

    public function getID()
    {
        return $this->id;
    }
}

$id = "df799fb47bc1e13f3e1c8b04ebd16a96";

$simplexml = simplexml_load_string($xml);
$result = $simplexml->xpath(sprintf('/storagehouse/item[@id="%s"]', $id));
if (!$result || count($result) !== 1) {
    throw new Exception(sprintf('Item with id "%s" does not exists or is not unique.', $id));
}
list($item) = $result;
$item->category = 'LCD Monitor';
echo $simplexml->asXML();


$doc = new DOMDocument();
$doc->loadXML($xml);
$xpath = new DOMXPath($doc);
$result = $xpath->query(sprintf('/storagehouse/item[@id="%s"]', $id));
if (!$result || $result->length !== 1) {
    throw new Exception(sprintf('Item with id "%s" does not exists or is not unique.', $id));
}
$item = $result->item(0);
$category = $xpath->query('./category', $item)->item(0);
$category->nodeValue = "LCD Monitor";
echo $doc->saveXML($item);


$repository = new Repository($xml);
$item = $repository->getItemByID($id);
$item->category = 'LCD Monitor';
$repository->saveChanges();
echo $repository->getXML();