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

说明

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

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

参数

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.

错误／异常

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.

返回值

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.

示例

示例 #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";

?>

以上示例会输出：

There are 2 english books

参见

DOMXPath::query() - Evaluates the given XPath expression

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用户贡献的备注 5 notes

down

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.

down

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])".

down

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


}

        }

    }

?>

down

aazaharov81 at gmail dot com ¶

10 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'));
?>

down

danny at webdevelopers dot eu ¶

5 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);
        }
?>