[RESOLVED] Error handling when missing XML elements?

[Dustie]

Hi all

Here's a chunk of test XML data I'm using:

<?xml version="1.0" encoding="iso-8859-1" ?>
<calendar>
  <gig>
    <date>Friday 5 August</date>
    <band>Depeche Mode</band>
    <time>8.30pm - 11:00pm</time>
    <website>http://depechemode.com</website>
  </gig>
  <gig>
    <date>Saturday 6 August</date>
    <band>Erasure</band>
    <time>8.30pm - 10:30pm</time>
    <website>http://erasure.com</website>
  </gig>
  <gig>
    <date>Sunday 7 August</date>
    <band>The Unknowns</band>
    <time>8.30pm - 10:30pm</time>
  </gig>
</calendar>

As you can see, in the last chunk of data, the <website> element is (deliberately) missing. The reason is, I want to be able to leave out elements and have my PHP coding be able to simply ignore elements that aren't there, rather than having to use an empty <website></website> (as I like making my life more complicated than it already is...) 😉

Here's the PHP code that's looping through and outputting the data:

$xmlDoc = new DOMDocument();
$xmlDoc->load('example.xml');
$xmlGigs = $xmlDoc->getElementsByTagName("gig");
$totalGigs = $xmlGigs->length;

for ($i=0; $i<$totalGigs; $i++)
	{
	echo ($xmlGigs->item($i)->getElementsByTagName("date")->item(0)->nodeValue) . "<br/>";
	echo ($xmlGigs->item($i)->getElementsByTagName("band")->item(0)->nodeValue) . "<br/>";
	echo ($xmlGigs->item($i)->getElementsByTagName("time")->item(0)->nodeValue) . "<br/>";
	echo ($xmlGigs->item($i)->getElementsByTagName("website")->item(0)->nodeValue) . "<br/>";
	echo ("<hr/>");
		}

And, at the last hurdle, it throws up an error saying:

Notice: Trying to get property of non-object....

Can anyone advise how I can do some simple clean Error Handling to detect that an XML Element doesn't exist and simply skip past it? I've been racking my brain for hours now but none of the approaches tried have worked.

Cheers 🙂

[bradgrafelman]

Rather than this long chain of object method calls:

$xmlGigs->item($i)->getElementsByTagName("date")->item(0)->nodeValue

break it up and check for points of failure.

For example, you might stop after the getElementsByTagName("date") call and check to see if the DOMNodeList object returned has value greater than 0 for the length property. If it doesn't, item(0) isn't going to get you an object (thus you'd be 'trying to get [the] property of [a] non-object').

[Dustie]

Thanks Brad! New code...

$xmlDoc = new DOMDocument();
$xmlDoc->load('example.xml');
$xmlGigs = $xmlDoc->getElementsByTagName("gig");
$totalGigs = $xmlGigs->length;

for ($i=0; $i<$totalGigs; $i++)
	{
	$date = $xmlGigs->item($i)->getElementsByTagName("date");
	$band = $xmlGigs->item($i)->getElementsByTagName("band");
	$time = $xmlGigs->item($i)->getElementsByTagName("time");
	$website = $xmlGigs->item($i)->getElementsByTagName("website");

if (($date->length) > 0)
	{
	echo ($date->item(0)->nodeValue) . "<br/>";
	}
if (($band->length) > 0)
	{
	echo ($band->item(0)->nodeValue) . "<br/>";
	}
if (($time->length) > 0)
	{
	echo ($time->item(0)->nodeValue) . "<br/>";
	}
if (($website->length) > 0)
	{
	echo ($website->item(0)->nodeValue) . "<br/>";
	}
echo ("<hr/>");
}

..it works a treat!!! 😃

[bradgrafelman]

Don't forget to mark this thread resolved (if it is) using the link on the Thread Tools menu above.

Also note that if what you're doing is the same for all of the node lists, you could save yourself a bit of typing by just gathering all of the node lists in an array and looping over that array, e.g.:

    $nodes = array();
    $nodes[] = $xmlGigs->item($i)->getElementsByTagName("date");
    $nodes[] = $xmlGigs->item($i)->getElementsByTagName("band");
    $nodes[] = $xmlGigs->item($i)->getElementsByTagName("time");
    $nodes[] = $xmlGigs->item($i)->getElementsByTagName("website");

foreach($nodes as $node
		if ($node->length > 0)
				{
				echo ($node->item(0)->nodeValue) . "<br/>";
				}

[Dustie]

Thanks a million Brad. Am still very new at all this but will hopefully refine my skills over time.. 🙂