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Retieving XML data

worldofwires
worldofwires asked
on
Medium Priority
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Last Modified: 2013-12-13
I'm using DomDocument to retrieve data from an XML file, my issue that the XML may not have all the data I'm requesting and consequently I'm getting errors along the lines of... Trying to get property of non-object.
I've tried a few workarounds like if isset and if($data=$doc->getElementsByTagName("pcap") but neither seem to be working. I'm not a complete idiot, what am I missing?
Thank is advance for any assistance or suggestions.
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Top Expert 2008

Commented:
>> Trying to get property of non-object.

This would happen when you try to read a property from something that is not an object. For example:

$a=0;
echo $a->b;

Could you post your code and some sample xml?

Author

Commented:
Hi, thanks for quick response.

I've included a snippet of the code I'm using and underneath the if statement is an example of what I've been trying to get around the issue. There is a sample xml file attached too, so if the car element for instance doesn't exisit, it would generate the error. I hope this makes sense.

if(file_exists('data/records/xml/'.$fn.'.xml')) {
  $doc = new DOMDocument();
  $doc->load('data/records/xml/'.$fn.'.xml');
 
  $data=$doc->getElementsByTagName("name");
  $arr['name']=array($data->item(0)->getAttribute("last"), $data->item(0)->getAttribute("first"));
 
  $data=$doc->getElementsByTagName("car");
  $arr['car']=$data->item(0)->nodeValue;
}
 
if($data=$doc->getElementsByTagName("car")) $arr['car']=$data->item(0)->nodeValue; else $arr['car']=0;

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sample.xml.txt
Top Expert 2008

Commented:
getElementsByTagName() returns a DOMNodeList, this object has a "length" property. Check if this is non-zero before trying to fetch anything from it.
if(file_exists('data/records/xml/'.$fn.'.xml')) {
  $doc = new DOMDocument();
  $doc->load('data/records/xml/'.$fn.'.xml');
 
  $data=$doc->getElementsByTagName("name");
  if($data->length)
    $arr['name']=array($data->item(0)->getAttribute("last"), $data->item(0)->getAttribute("first"));
  else 
    $arr['name']=false;
 
  $data=$doc->getElementsByTagName("car");
  if($data->length)
    $arr['car']=$data->item(0)->nodeValue;
  else 
    $arr['car']=0;
}
 
# The problem with this:
if($data=$doc->getElementsByTagName("car")) 
  $arr['car']=$data->item(0)->nodeValue; else $arr['car']=0;
# ...is that getElementsByTagName() allways returns an object (DOMNodeList), even if no nodes was found.
# Thus, the if-statement is allways true.

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Author

Commented:
Thanks cxr,

Just to check I've got this, so in my code I can do $data=$doc->getElementsByTagName("car"); And then do an IF statement saying if $data!=0 then use nodeValue, else it's 0?

It seems to work, I'm just clarifying I understand what's going on. Also, in your opinion, is there a problem with constantly reusing the $data value for each getElementByTagName?

Much appreciated.
Top Expert 2008
Commented:
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Most Valuable Expert 2011
Author of the Year 2014
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Author

Commented:
Thanks both,

I've used the SimpleXML on another XML function but got a little lost when using attributes. I like to keep things simple. :) I may rewrite but in teh meantime, xcr has solved my error generating problem.

Excellent, thaks guys. This site rocks.
Most Valuable Expert 2011
Author of the Year 2014

Commented:
Thanks for the points.  The rule of attributes is that they are array indexes.  See line 33 of the post above for the way to isolate those.  Best regards, ~Ray
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