SunshinePHP Developer Conference 2015

DOMDocument::getElementById

(PHP 5)

DOMDocument::getElementByIdSearches for an element with a certain id

Description

DOMElement DOMDocument::getElementById ( string $elementId )

This function is similar to DOMDocument::getElementsByTagName but searches for an element with a given id.

For this function to work, you will need either to set some ID attributes with DOMElement::setIdAttribute or a DTD which defines an attribute to be of type ID. In the later case, you will need to validate your document with DOMDocument::validate or DOMDocument->validateOnParse before using this function.

Parameters

elementId

The unique id value for an element.

Return Values

Returns the DOMElement or NULL if the element is not found.

Examples

Example #1 DOMDocument->getElementById() Example

<?php

$doc 
= new DomDocument;

// We need to validate our document before refering to the id
$doc->validateOnParse true;
$doc->Load('book.xml');

echo 
"The element whose id is books is: " $doc->getElementById('books')->tagName "\n";

?>

The above example will output:

The element whose id is books is: chapter

See Also

add a note add a note

User Contributed Notes 9 notes

up
12
ed at edgiardina dot com
4 years ago
Please note that if your HTML does not contain a doctype declaration, then getElementById will always return null.
up
6
paradox_haze at live dot de
4 years ago
Had some issues with getElementById() while searching for a specific element in a XHTML document.
I wrote a small function what was solving my problem:

<?php
function getElementById($id)
{
   
$xpath = new DOMXPath($this->domDocument);
    return
$xpath->query("//*[@id='$id']")->item(0);
}
?>
up
1
Anonymous
8 years ago
If you're trying to use getElementById with a xml file validated on a xsd file you must first use the schemaValidate function or getElementById will return null
Example:

  $dom = new DomDocument();
  $dom->load("users.xml");
  $dom->schemaValidate("users.xsd");

  $curruser = $dom->getElementById($user->name);
up
1
carl2088 at gmail dot com
5 years ago
From my experience, getElementById seem to work fine without any setups if you have loaded a HTML document. But in order for getElementById to work with a simple XML document that you've "constructed", you have to set up the id with "xml:" prefix and use setIdAttribute on the element you created or it won't work. See following example, hope this will save someone's frustration. If you have loaded the xml file, then all you have to make sure is the ID has a xml: prefix for the attribute.  But if you start to append the XML document, don't forget to setIdAttribute on the id name or those elements or getElementById will return null when you try to find them.

<?php

   
/* test.xml
    <?xml version="1.0" encoding="utf-8"?>
    <root>
        <child xml:id="id_xxxxxx" status="partial">
            <sub_child>Some Data</sub_child>
        </child>
    </root>
    */

   
$xmlDom = new DOMDocument('1.0', 'utf-8');
   
$xmlDom->formatOutput = true;                        // we want a nice output

    // create a root
   
$eltRoot = $xmlDom->createElement("root");
   
$xmlDom->appendChild($eltRoot);

   
$eltChild = $xmlDom->createElement("child");
   
$eltRoot->appendChild($eltChild);
   
   
// add a id attribute
   
$attr = $xmlDom->createAttribute("xml:id");    // needs xml prefix or getElementById won't work
   
$eltChild->appendChild($attr);
   
   
/// create the text node and append to the created element
   
$tNode = $xmlDom->createTextNode("id_8120528");
   
$attr->appendChild($tNode);
   
$eltChild->setIdAttribute("xml:id", true);    // VERY IMPORT or getElementById won't work
   
    // add a id attribute
   
$attr = $xmlDom->createAttribute("status");
   
$eltChild->appendChild($attr);
   
   
/// create the text node and append to the created element
   
$tNode = $xmlDom->createTextNode("partial");
   
$attr->appendChild($tNode);   
   
   
// add a subchild
   
$eltSub = $xmlDom->createElement("sub_child");
   
$eltChild->appendChild($eltSub);
   
   
$tNode = $xmlDom->createTextNode("Some Data");
   
$eltSub->appendChild($tNode);

   
$id = null;
   
$id = $xmlDom->getElementById("id_8120528");
   
   
assert ($id != null);
   
   
$strId = $id->getAttribute("xml:id"); // bug? empty
   
$strStatus = $id->getAttribute("status"); // this works!
   
   
assert ($id !=null);
   
   
$xmlDom->save("./_data/test.xml");
   
   
$xmlDom->load("./_data/test.xml"); // reloading fixes the problem
   
   
$nodeRoot = $xmlDom->getElementsByTagName("root");
    if (
$nodeRoot->length > 0) {
       
$eltRoot = $nodeRoot->item(0);   
    }
   
   
assert($eltRoot != null);
   
   
$id = null;
   
$id = $xmlDom->getElementById("id_8120528");

   
assert ($id != null);

   
$strId = $id->getAttribute("xml:id"); // this works now!
   
$strStatus = $id->getAttribute("status"); // this works!
       
   
?>
up
1
guillaume dot crico at gmail dot com
6 years ago
You don't want to use "xml:id" ?
Here is the relaxNG trick (with a generic schema):
(tested with libxml 2.6.26)

<?php
$doc
= new DOMDocument();
$doc->load(...);

$rng = '
<grammar xmlns="http://relaxng.org/ns/structure/1.0" datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
    <start>
        <element>
            <anyName/>
            <ref name="anythingID"/>
        </element>
    </start>
    <define name="anythingID">
        <zeroOrMore>
            <choice>
                <element>
                    <anyName/>
                    <ref name="anythingID"/>
                </element>
                <attribute name="id">
                    <data type="ID"/>
                </attribute>
                <zeroOrMore>
                    <attribute><anyName/></attribute>
                </zeroOrMore>
                <text/>
            </choice>
        </zeroOrMore>
    </define>
</grammar>
'
;

$doc->relaxNGValidateSource($rng);
var_dump($doc->getElementById('id1'));
?>


Note that ID values must be valid ones :
  - integers do no work!
  - @see http://www.w3.org/TR/REC-xml/#id
  - => (Letter | '_' | ':') ( Letter | Digit | '.' | '-' | '_' | ':' | CombiningChar | Extender  )*
up
1
simon at somewhere dot com
7 years ago
SAVE YOURSELF A MAJOR HEADACHE AND A LOT OF SEARCHING THROUGH DOCUMENTATION -

Instead of using $object->setAttribute('id', 'id_name_here')
USE THIS: $object->setAttribute('xml:id', 'id_name_here')

Then, to get the node value: $domDocumentObject->getElementById('id_name_here');

The xml:id attribute should AUTOMATICALLY be defined!!

Woohoo!  That was easy......
up
0
jonbarnett at gmail dot com
7 years ago
If your XML document does not have a DTD that defines the "id" attribute as an ID, then the easiest thing to do is to use XPath->query() to find an element that matches "//[@id='x']"
up
0
Tangui dot Le-Pense at laposte dot net
8 years ago
Validating a document from a DTD so as to use getElementById is sometimes impossible (for example when the head and body elements are not included yet in a XHtml document : the validation failed).
Fortunately, xml:id is supported by this function :)
That may be useful.
http://www.w3.org/TR/xml-id/
up
0
bart at mediawave dot nl
9 years ago
It seems getElementById works fine without setting validateOnParse to true. Which is nice since setting this to true caused some performance problems with my script.
To Top