DOMXPath::evaluate

(PHP 5 >= 5.1.0, PHP 7, PHP 8)

DOMXPath::evaluate Evalúa la expresión XPath dada y devuelve un resultado escrito si es posible

Descripción

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

Ejecuta la expresión XPath dada por expression y devuelve un resultado escrito si es posible.

Parámetros

expression

La expresión XPath a ejecutar.

contextNode

El parámetro opcional contextNode se puede especificar para hacer consultas XPath relativas. Por omisión, las consultas son relativas al elemento raíz.

registerNodeNS

El parámetro opcional registerNodeNS puede ser especificado para deshabilitar el registro automático del nodo de contexto.

Valores devueltos

Devuelve un resultado escrito si es posible o un objeto DOMNodeList que contiene todos los nodos coincidentes con la expresión XPath dada por expression.

Si el parámetro expression está malformado o el parámetro contextNode es inválido, DOMXPath::evaluate() devuelve false.

Ejemplos

Ejemplo #1 Obtener el número de todos los libros en inglés

<?php

$doc
= new DOMDocument;

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

$xpath = new DOMXPath($doc);

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

// nuestra consulta es relativa al nodo tbody
$consulta = 'count(row/entry[. = "en"])';

$entradas = $xpath->evaluate($consulta, $tbody);
echo
"Hay $entradas libros en inglés\n";

?>

El resultado del ejemplo sería:

Hay 2 libros en inglés

Ver también

add a note

User Contributed Notes 5 notes

up
4
daniel at danielnorton dot com
13 years ago
Note that this method does not provide any means to distinguish between a successful result that returns FALSE and an error.

For example, this will succeed and return FALSE:

<?php $xpath->evaluate("1 = 0"); ?>

One workaround when you know you are expecting a Boolean is to wrap the result with string(). e.g.

<?php $xpath->evaluate("string(1 = 0)"); ?>

This will return a string "false" on success, or the Boolean FALSE on error.
up
4
Damien Bezborodov
13 years ago
If your expression returns a node set, you will get a DOMNodeList instead of a typed result. Instead, try modifying your expression from "//node[1]" to "string(//node[1])".
up
4
yuriucsal at NOSPAM dot yahoo dot com dot br
19 years ago
this class can substitute the method evaluate while it is not validated. Made for Yuri Bastos and Jo�o Gilberto Magalh�es.

<?php

class XPtahQuery
{
// function returns a DOMNodeList from a relative xPath
public static function selectNodes($pNode, $xPath)
{

$pos = strpos(self::getFullXpath($pNode),"/",1);
$xPathQuery = substr(self::getFullXpath($pNode),$pos);//to paste /#document[1]/
$xPathQueryFull = $xPathQuery. $xPath;
$domXPath = new DOMXPath($pNode->ownerDocument);
$rNodeList = $domXPath->query($xPathQueryFull);

return
$rNodeList;
}
// function returns a DOMNode from a xPath from other DOMNode
public static function selectSingleNode($pNode, $xPath)
{

$pos = strpos(self::getFullXpath($pNode),"/",1);
$xPathQuery = substr(self::getFullXpath($pNode),$pos);//to paste /#document[1]/
$xPathQueryFull = $xPathQuery. $xPath;
$domXPath = new DOMXPath($pNode->ownerDocument);
$rNode = $domXPath->query($xPathQueryFull)->item(0);

return
$rNode;
}
//utilitaries functions off selectSingleNode
private function getNodePos($pNode, $nodeName)
{
if(
$pNode == null)
{
return
0;
}
else
{
$var = 0;
if (
$pNode->previousSibling != null)
{
if (
$pNode->previousSibling->nodeName == $nodeName)
{
$var = 1;
}
}
return
self::getNodePos($pNode->previousSibling, $nodeName) + $var;
}
}
//utilitaries functions off selectSingleNode
private function getFullXpath($pNode)
{
if(
$pNode == null)
{
return
"";
}
else
{

return
self::getFullXpath($pNode->parentNode) . "/" . $pNode->nodeName . "[" .strval(self::getNodePos($pNode, $pNode->nodeName)+1) . "]";//+1 to get the real xPath index

}
}
}
?>
up
1
aazaharov81 at gmail dot com
9 years ago
To query DOMNodes by their HTML classes, use such snippet
<?php

// CssClassXPathSelector
function ccxs($class) {
return
'[contains(concat(" ", normalize-space(@class), " "), " ' . $class . ' ")]';
}

// then just
$domitems = $this->xpath("//*[@id='searchResultsRows']//a" . ccxs('listing_row'));
?>
up
1
danny at webdevelopers dot eu
4 years ago
The only way how to distinguish FALSE returned value from syntax error FALSE is to re-run the XPath expression wrapped in string() function. If must return empty string. If it returns FALSE again then it is an error.

<?php

$ret
=$this->xp->evaluate($eval, $context);

// Error detection: DOMXPath::evaluate() returns FALSE on error
// so does DOMXPath::evaluate("boolean(/nothing)")
// @workaround webdevelopers.eu
if ($ret === false && $this->xp->evaluate("string($eval)", $context) === false) {
throw new
Exception("Invalid XPath expression ".json_encode($eval), 3491);
}
?>
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