Working through the XML Dom? - php

Question

I am new to the xml dom and I am trying to to retrieve the value in the '' tags.
The problem is I am not sure how to work down to that level in the dom.
I have tried to do something like this:
itemXML.getElementById("gender").getElementsByTagName("item").nodeValue;
But that returns 'undefined', how would I specify which tag I want to retrieve the value of?
Below is the contents of my xml document:
<dataFields>
<items id="gender">
<item>Male</item>
<item>Female</item>
</items>
<items id="age">
<item>0-3 years</item>
<item>3-6 years</item>
<item>7-16 years</item>
<item>17-25 years</item>
<item>26-40 years</item>
<item>41-65 years</item>
<item>65+ years</item>
</items>

Answer 1

$xpath = new DOMXPath($itemXML);
$genderItems = $xpath->query('/dataFields/items[#id="gender"]/item');
foreach ($genderItems as $genderItem) {
echo $genderItem->nodeValue . "\n"; // "Male", "Female"
}

Answer 2

$items = $doc->getElementsByTagName('item');

Answer 3

The id attribute in XML without a namespace prefix is just a normal attribute, only in html it is the identifier. So in xml documents, the attribute name would have to be "xml:id" to be found by getElementById(). The getElementsByTagName() method returns a list of element nodes, not just one. You will have to use foreach() or the item() method to access the elements in the list.
But here is an easier way. DOMXpath:evaluate() allows you to use xpath expression to fetch nodes and values from a DOM.
Here is some demo source:
$xml = <<<'XML'
<dataFields>
<items id="gender" xml:id="xml_gender">
<item>Male</item>
<item>Female</item>
</items>
<items id="age">
<item>0-3 years</item>
<item>3-6 years</item>
<item>7-16 years</item>
<item>17-25 years</item>
<item>26-40 years</item>
<item>41-65 years</item>
<item>65+ years</item>
</items>
</dataFields>
XML;
$dom = new DOMDocument();
$dom->loadXml($xml);
// difference between id and xml:id
var_dump(
$dom->getElementById('gender'),
get_class($dom->getElementById('xml_gender'))
);
/* Output:
NULL
string(10) "DOMElement"
*/
// getElementsByTagName returns a node list
var_dump(
get_class($dom->getElementById('xml_gender')->getElementsByTagName('item'))
);
/* Output:
NULL
string(11) "DOMNodeList"
*/
// you can iterate node lists
foreach ($dom->getElementById('xml_gender')->getElementsByTagName('item') as $item) {
var_dump($item->nodeValue);
}
/* Output:
string(4) "Male"
string(6) "Female"
*/
// it is easier with xpath
$xpath = new DOMXpath($dom);
foreach ($xpath->evaluate('//items[#id = "gender"]/item') as $item) {
var_dump($item->nodeValue);
}
/* Output:
string(4) "Male"
string(6) "Female"
*/
// DOMXpath::evaluate() can be used to fetch values directly, too.
var_dump(
$xpath->evaluate('string(//items[#id = "gender"]/item[2])')
);
/* Output:
string(6) "Female"
*/