XPath query with PHP

Question

Here's the XML code i'm working with:

<inventory>
        <drink>
                <lemonade supplier="mother" id="1">
                        <price>$2.50</price>
                        <amount>20</amount>
                </lemonade>
                <lemonade supplier="mike" id="4">
                        <price>$3.00</price>
                        <amount>20</amount>
                </lemonade>
                <pop supplier="store" id="2">
                        <price>$1.50</price>
                        <amount>10</amount>
                </pop>
        </drink>
</inventory>

Then i wrote a simple code to practice working with XPath:

<?php
        $xmldoc = new DOMDocument();
        $xmldoc->load('sample.xml');

        $xpathvar = new Domxpath($xmldoc);

        $queryResult = $xpathvar->query('//lemonade/price');
        foreach($queryResult as $result){
                echo $result->textContent;
        }
?>

That code is working well, outputting all the lemonade price values as expected. Now when i change the query string to select only the elements with an attribute set to a certain value, like

//lemonade[supplier="mother"]/price

or

//lemonade[id="1"]/price

it won't work, no output at all. What am i doing wrong?

Answer 1

Try this:

//lemonade[@id="1"]/price

or

//lemonade[@supplier="mother"]/price

Without the "@" it looks for child elements with that name instead of attributes.

Answer 2

you have to use the @ sign to indicate attribute within the predicate like so: //lemonade[@supplier="mother"]/price, that's all.

Answer 3

This is only tangentially related, but when you use XPath on a document for which you know the structure, don't use "//some-element-name". It's very nice for a quick example, but when you hit a huge xml file with that query, particularly if it is followed by something complex, you will quickly run into performance issues.

inventory/drink/lemonade[@supplier="mother"]/price