(PHP 5 >= 5.1.0, PHP 7, PHP 8)
DOMXPath::evaluate — Evalúa la expresión XPath dada y devuelve un resultado escrito si es posible
$expression, ?DOMNode $contextNode = null, bool $registerNodeNS = true): mixed
Ejecuta la expresión XPath dada por expression y devuelve
un resultado escrito si es posible.
expressionLa 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.
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.
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
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 $xpath->evaluate("string(1 = 0)"); ?>
This will return a string "false" on success, or the Boolean FALSE on error.If your expression returns a node set, you will get a DOMNodeList instead of a typed result. Instead, try modifying your expression from "//node[1]" to "string(//node[1])".this class can substitute the method evaluate while it is not validated. Made for Yuri Bastos and Jo�o Gilberto Magalh�es.
<?php
class XPtahQuery
{
// function returns a DOMNodeList from a relative xPath
public static function selectNodes($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, $pNode->nodeName)+1) . "]";//+1 to get the real xPath index
}
}
}
?>To query DOMNodes by their HTML classes, use such snippet
<?php
// CssClassXPathSelector
function ccxs($class) {
return '[contains(concat(" ", normalize-space(@class), " "), " ' . $class . ' ")]';
}
// then just
$domitems = $this->xpath("//*[@id='searchResultsRows']//a" . ccxs('listing_row'));
?>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);
}
?>