PHP Unconference Europe 2015

DOMDocument::getElementById

(PHP 5)

DOMDocument::getElementByIdCherche un élément avec un certain identifiant

Description

public DOMElement DOMDocument::getElementById ( string $elementId )

Cette fonction est similaire à la fonction DOMDocument::getElementsByTagName mais cherche un élément avec un identifiant donné.

Pour que cette fonction fonctionne, vous devez soit définir les attributs ID avec DOMElement::setIdAttribute ou définir une DTD qui définit un attribut devant être de type ID. Dans le dernier cas, vous devez valider votre document avec DOMDocument::validate ou DOMDocument::$validateOnParse avant d'utiliser cette fonction.

Liste de paramètres

elementId

La valeur de l'identifiant unique pour un élément.

Valeurs de retour

Retourne un DOMElement ou NULL si l'élément n'est pas trouvé.

Exemples

Exemple #1 Exemple avec DOMDocument::getElementById()

L'exemple suivant utilise le fichier book.xml, dont le contenu est :

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE books [
  <!ELEMENT books   (book+)>
  <!ELEMENT book    (title, author+, xhtml:blurb?)>
  <!ELEMENT title   (#PCDATA)>
  <!ELEMENT blurb   (#PCDATA)>
  <!ELEMENT author  (#PCDATA)>
  <!ATTLIST books   xmlns        CDATA  #IMPLIED>
  <!ATTLIST books   xmlns:xhtml  CDATA  #IMPLIED>
  <!ATTLIST book    id           ID     #IMPLIED>
  <!ATTLIST author  email        CDATA  #IMPLIED>
]>
<?xml-stylesheet type="text/xsl" href="style.xsl"?>
<books xmlns="http://books.php/" xmlns:xhtml="http://www.w3.org/1999/xhtml">
  <book id="php-basics">
    <title>PHP Basics</title>
    <author email="jim.smith@basics.php">Jim Smith</author>
    <author email="jane.smith@basics.php">Jane Smith</author>
    <xhtml:blurb><![CDATA[
<p><em>PHP Basics</em> provides an introduction to PHP.</p>
]]></xhtml:blurb>
  </book>
  <book id="php-advanced">
    <title>PHP Advanced Programming</title>
    <author email="jon.doe@advanced.php">Jon Doe</author>
  </book>
</books>
<?php

$doc 
= new DomDocument;

// Nous devons valider notre document avant de nous référer à l'ID
$doc->validateOnParse true;
$doc->Load('book.xml');

echo 
"L'élément dont l'ID est 'php-basics' est : " $doc->getElementById('php-basics')->tagName "\n";

?>

L'exemple ci-dessus va afficher :

L'élément dont l'ID est 'php-basics' est : chapter

Voir aussi

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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
8 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.
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