Question

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Xpath fails if an element has a a xmlns attribute

I have been trying for a long time to extract a string from the following xml with no luck
http://chris.photobooks.com/xml/default.htm?state=8T

I am trying to get the ASIN number of a book and I have tried

$xpath->query('//MarketplaceASIN/ASIN')->item(0)->nodeValue;

and

$xpath->query('/GetMatchingProductResponse/GetMatchingProductResult[1]/Product/Identifiers/MarketplaceASIN/ASIN')->item(0)->nodeValue;

but neither seem to work, what am I doing wrong here?

Answer 1

The elements in that document are bound to the namespace http://mws.amazonservices.com/schema/Products/2011-10-01.

You may have missed it because it does not use a namespace-prefix and the xmlns="http://mws.amazonservices.com/schema/Products/2011-10-01" just looks like an attribute, but namespace attributes are special.

All of the descendant elements inherit that namespace. You will want to register the namespace with a namespace-prefix and adjust your XPath:

$rootNamespace = $xml->lookupNamespaceUri($xml->namespaceURI); 
$xpath->registerNamespace('a', $rootNamespace); 
$elementList = $xpath->query('//a:MarketplaceASIN/a:ASIN');

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Or you could use a more generic XPath that matches on elements and uses a predicate filter to match the local-name() and namespace-uri():

//*[local-name()='MarketplaceASIN' and namespace-uri()='http://mws.amazonservices.com/schema/Products/2011-10-01']/*[local-name()='ASIN' and namespace-uri()='http://mws.amazonservices.com/schema/Products/2011-10-01']