DOMDocument::getElementById

(PHP 5, PHP 7, PHP 8)

DOMDocument::getElementById — id に対応する要素を検索する

説明

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

この関数は、 DOMDocument::getElementsByTagName と同じですが、指定した ID から要素を検索する点が違います。

この関数を動作させるには、何らかの ID 属性を DOMElement::setIdAttribute で設定するか、あるいは DTD で ID 型の属性を定義する必要があります。後者の場合は、 DOMDocument::validate あるいは DOMDocument::$validateOnParse を使用してドキュメントを検証する必要があります。

パラメータ

elementId: 要素の ID。

戻り値

DOMElement、あるいは要素が見つからなかった場合は null を返します。

例

例1 DOMDocument::getElementById() の例

次の例では、以下のような内容の book.xml を使います。

<?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;

// ID を参照する前に、ドキュメントを検証する必要があります
$doc->validateOnParse = true;
$doc->Load('book.xml');

echo "ID が 'php-basics' の要素は " . $doc->getElementById('php-basics')->tagName . " です。\n";

?>

上の例の出力は以下となります。

ID が 'php-basics' の要素は book です。

参考

DOMDocument::getElementsByTagName() - 指定したローカルタグ名に対応するすべての要素を検索する

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User Contributed Notes 10 notes

down

ed at edgiardina dot com ¶

14 years ago


Please note that if your HTML does not contain a doctype declaration, then getElementById will always return null.

down

carl2088 at gmail dot com ¶

15 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!
        
    
?>

down

paradox_haze at live dot de ¶

14 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);
}
?>

down

simon at somewhere dot com ¶

17 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......

down

Hoi ¶

4 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.

down

Anonymous ¶

19 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);

down

bart at mediawave dot nl ¶

19 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.

down

-1

Tangui dot Le-Pense at laposte dot net ¶

18 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/

down

-3

jonbarnett at gmail dot com ¶

18 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']"

down

-2

guillaume dot crico at gmail dot com ¶

16 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  )*

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