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DOMDocument::getElementById Ищет элемент с определённым идентификатором


public DOMDocument::getElementById(string $elementId): ?DOMElement

Эта функция похожа на DOMDocument::getElementsByTagName, но ищет элемент с заданным идентификатором.

Для работы этой функции необходимо установить атрибуты идентификаторов с помощью DOMElement::setIdAttribute, либо DTD, который определяет атрибут идентификатора типа. В последнем случае перед использованием этой функции вам необходимо будет проверить документ с помощью DOMDocument::validate или DOMDocument::$validateOnParse.

Список параметров


Уникальный значение идентификатора элемента.

Возвращаемые значения

Возвращает объект DOMElement или null, если элемент не найден.


Пример #1 Пример использования DOMDocument::getElementById()

Следующие примеры используют файл book.xml, который содержит следующие данные:

<?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="">
  <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>
<p><em>PHP Basics</em> provides an introduction to PHP.</p>
  <book id="php-advanced">
    <title>PHP Advanced Programming</title>
    <author email="jon.doe@advanced.php">Jon Doe</author>

= new DomDocument;

// Нужно проверить документ перед тем как ссылаться по идентификатору
$doc->validateOnParse = true;

"Элемент с идентификатором 'php-basics': " . $doc->getElementById('php-basics')->tagName . "\n";


Результат выполнения данного примера:

Элемент с идентификатором 'php-basics': book

Смотрите также

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User Contributed Notes 10 notes

ed at edgiardina dot com
12 years ago
Please note that if your HTML does not contain a doctype declaration, then getElementById will always return null.
carl2088 at gmail dot com
13 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.


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

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

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

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

$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->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!
paradox_haze at live dot de
12 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:

function getElementById($id)
$xpath = new DOMXPath($this->domDocument);
simon at somewhere dot com
16 years ago

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......
2 years ago
To set a hidden id that can be used by $dom->getElementById() apply setAttribute('id', true) as in the following example

                    $createItemNode = function ($data) use ($dom) {
                        $node = $dom->createElement("Item");
                        $node->setAttribute('id', $data->id);
                        $node->setAttribute('hed', $data->hed);
                        $node->setAttribute('run_time', $data->run_time);
                        $node->setAttribute('date', $data->date);

                        // Internally mark the id as 'xml:id' for getElementById to work. Adding xml:id manually to the tag will cause loadXML to throw an error DOMDocument: xml:id is not a NCName in Entity
                        $node->setIdAttribute('id', true);

                        return $node;

With $node->setIdAttribute('id', true), $dom->getElementById($id) will work

When you do $dom->saveXML(), the final doc will not contain any xml:id attribute.
17 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

  $dom = new DomDocument();

  $curruser = $dom->getElementById($user->name);
bart at mediawave dot nl
17 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.
Tangui dot Le-Pense at laposte dot net
16 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.
jonbarnett at gmail dot com
16 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']"
guillaume dot crico at gmail dot com
14 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)

= new DOMDocument();

$rng = '
<grammar xmlns="" datatypeLibrary="">
            <ref name="anythingID"/>
    <define name="anythingID">
                    <ref name="anythingID"/>
                <attribute name="id">
                    <data type="ID"/>


Note that ID values must be valid ones :
  - integers do no work!
  - @see
  - => (Letter | '_' | ':') ( Letter | Digit | '.' | '-' | '_' | ':' | CombiningChar | Extender  )*
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