DOMXPath::evaluate

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

DOMXPath::evaluate Evaluates the given XPath expression and returns a typed result if possible

Beschreibung

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

Executes the given XPath expression and returns a typed result if possible.

Parameter-Liste

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

Legt fest, ob die Namensraum-Präfixe innerhalb des Geltungsbereichs des Kontextknotens automatisch im DOMXPath-Objekt registriert werden sollen. Dies kann verwendet werden, damit DOMXPath::registerNamespace() nicht manuell für jeden Namensraum innerhalb des Geltungsbereichs aufgerufen werden muss. Wenn es einen Konflikt zwischen Namensraum-Präfixen gibt, wird nur das in der Reihenfolge nächste Namensraum-Präfix registriert.

Rückgabewerte

Returns a typed result if possible or a DOMNodeList containing all nodes matching the given XPath expression.

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

Beispiele

Beispiel #1 Getting the count of all the english books

<?php

$doc
= new DOMDocument;

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

$xpath = new DOMXPath($doc);

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

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

$entries = $xpath->evaluate($query, $tbody);
echo
"There are $entries english books\n";

?>

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

There are 2 english books

Siehe auch

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User Contributed Notes 5 notes

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
3
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
3
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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