Simple XML - How to select all elements which have a specific attribute value

Question

A user can select a performance, so the performance elements have unique ID's. I want to basically say:

Select all reservations->reservation['seat'] FROM performances->performance['id=2'].

Hope that makes sense, I really am struggling with selections in simple XML.

Thanks in advance, Henry.

    <performances>
                <performance id="7" time="12:00" day="Monday" month="June" year="2010">
                    <reservations>
                        <reservation seat="a7"/>
                        <reservation seat="a2"/>
                        <reservation seat="a3"/>
                    </reservations>
                </performance>
                <performance id="8" time="12:00" day="Tuesday" month="June" year="2010">
                    <reservations>
                        <reservation seat="a8"/>
                    </reservations>
                </performance>
</performances>

Extra Info:

I am currently using: echo $xml2->show->performances->performance['0']->reservations->reservation['seat']

This gets one reservation from the first performance, but I want all reservations from the performance with the id of '3' for example.

Answer 1

Your "SQL":

SELECT reservations->reservation['seat'] FROM performances->performance['id=2']

can be reformulated as:

FROM performances->performance['id=2'] SELECT reservations->reservation['seat'] 

can be reformulated as XPath:

//performances/performance[@id=2]/reservations/reservation/@seat

Ant that's what you need. Look at SimpleXML's xpath() method.

Answer 2

<?php
// create a variable repsresenting the xml to parse through
$string = '<performances>
            <performance id="7" time="12:00" day="Monday" month="June" year="2010">
                <reservations>
                    <reservation seat="a7"/>
                    <reservation seat="a2"/>
                    <reservation seat="a3"/>
                </reservations>
            </performance>
            <performance id="8" time="12:00" day="Tuesday" month="June" year="2010">
                <reservations>
                    <reservation seat="a8"/>
                </reservations>
            </performance>
</performances>';

// create a variable representing a SimpleXMLElement instance
$xml = simplexml_load_string($string);

// create a variable representing the desired results, using the xpath method for
// the SimpleXMLElement instance previously created.
$results = $xml->xpath('//performances/performance[@id=2]/reservations/reservation/@seat');

?>

Sorry to steal Tomalak's thunder here. Some folks need it spelled out sometimes.