DOMXPath::query

(PHP 5, PHP 7, PHP 8)

DOMXPath::query — Evaluates the given XPath expression

Description

public DOMXPath::query(string $expression, ?DOMNode $contextNode = null, bool $registerNodeNS = true): mixed

Executes the given XPath expression.

Parameters

expression

The XPath expression to execute.

contextNode

The optional contextNode can be specified for doing relative XPath queries. By default, the queries are relative to the root element.

registerNodeNS

Whether to automatically register the in-scope namespace prefixes of the context node to the DOMXPath object. This can be used to avoid needing to call DOMXPath::registerNamespace() manually for each in-scope namespaces. When a namespace prefix conflict exists, only the nearest descendant namespace prefix is registered.

Return Values

Returns a DOMNodeList containing all nodes matching the given XPath expression. Any expression which does not return nodes will return an empty DOMNodeList.

If the expression is malformed or the contextNode is invalid, DOMXPath::query() returns false.

Errors/Exceptions

The following errors are possible when using an expression that invokes PHP callbacks.

  • Throws an Error if a PHP callback is invoked but there were no callbacks registered, or if the named callback was not registered.
  • Throws a TypeError if the php:function syntax is used and the handler name is not a string.
  • Throws an Error if a non-DOM object was returned from a callback.

Examples

Example #1 Getting all the english books

<?php

$doc = new DOMDocument;

// We don't want to bother with white spaces
$doc->preserveWhiteSpace = false;

$doc->load('examples/book-docbook.xml');

$xpath = new DOMXPath($doc);

// We start from the root element
$query = '//book/chapter/para/informaltable/tgroup/tbody/row/entry[. = "en"]';

$entries = $xpath->query($query);

foreach ($entries as $entry) {
echo "Found {$entry->previousSibling->previousSibling->nodeValue}," .
" by {$entry->previousSibling->nodeValue}\n";
}
?>

The above example will output:

Found The Grapes of Wrath, by John Steinbeck
Found The Pearl, by John Steinbeck

We can also use the contextNode parameter to shorten our expression:

<?php

$doc = new DOMDocument;
$doc->preserveWhiteSpace = false;

$doc->load('examples/book-docbook.xml');

$xpath = new DOMXPath($doc);

$tbody = $doc->getElementsByTagName('tbody')->item(0);

// our query is relative to the tbody node
$query = 'row/entry[. = "en"]';

$entries = $xpath->query($query, $tbody);

foreach ($entries as $entry) {
echo "Found {$entry->previousSibling->previousSibling->nodeValue}," .
" by {$entry->previousSibling->nodeValue}\n";
}
?>

See Also