xml parsing xpath error using php

Question

I am attempting to use xpath to run a program and parse out xml data for repricing books. However, when I run the program I get the following errors:

PHP Warning:  SimpleXMLElement::xpath() [<a href='simplexmlelement.xpath'>simplexmlelement.xpath</a>]: Invalid expression

and

PHP Warning:  SimpleXMLElement::xpath() [<a href='simplexmlelement.xpath'>simplexmlelement.xpath</a>]: xmlXPathEval: evaluation failed

both on line 242 which is the line of $result...:

//function to check if child nodes exist for pricing
function xml_child_exists($xml, $childpath)
 {
$result = $xml->xpath($childpath);
 if (isset($result)) {
    return true;
} else {
    return false;
}

}

This function is run here:

// check to see if there are values
        if(xml_child_exists($parsed_xml, $current->AttributeSets->children('ns2', true)->ItemAttributes->ListPrice->Amount))
           { 
            $listPrice = $current->AttributeSets->children('ns2', true)->ItemAttributes->ListPrice->Amount;
          } else {
            $listPrice = 0;
          }

Then I finally am ending up with:

PHP Fatal error:  Call to a member function children() on a non-object in repricemws.php on line 67

Line 67 is where the function is being called.

What is wrong with this code and how do I make it so that it will run correctly?

Marc B · Accepted Answer · 2012-07-19 16:27:52Z

1

Does $current->AttributeSets->children('ns2', true)->ItemAttributes->ListPrice->Amount contain a valid XPath expression?

From the looks of that call chain, you're pulling out a single value, e.g. '5.00' and passing that directly to the xpath query executor. That's not going to work, and produce your error messages.

followup:

ok, so Amount is a price, so it's something like $5.00 or 5.00, right? That means you're using that exact string as your xpath query, basically doing:

$result = $xml->xpath('$5.00');

That is NOT a valid xpath expression. So $result is NOT a list of matching nodes in the document, it's actually going to be a boolean FALSE.

You then do an isset() on that value. The variable IS set (to boolean false), so your function returns TRUE.

edited Jul 19, 2012 at 16:27

answered Jul 19, 2012 at 16:12

Marc B

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3 Comments

Jim Over a year ago

Yes, it is a valid XPath expression and it is supposed to pull out a single value. How should this be written to execute correctly?

Marc B Over a year ago

...->Amount should return something like //div or whatever. What is it returning now?

Jim Over a year ago

Amount is returning the price of the book. If you mean from the function, it is returning true if there is a price and false if there is none.

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