Add multiple attributes to a child in SimpleXMLElement

Add multiple attributes to a child in SimpleXMLElement

I want to add multiple attributes to a child in SimpleXMLElement so it
will look like this:
<data>
<photo>
<file size="3309519" size="JPG">P1270081</file>
</photo>
</data>
As it is right now in my code, I can only add one attribute per child as
the code below shows.
$xml = new SimpleXMLElement('<data/>');
$photo = $xml->addChild('photo');
$photo->addChild('file', 'P1270081')->addAttribute('size', '3309519');
$photo->addChild('uploaded', '2013-09-01 15:23:10')->addAttribute('by',
'edgren');
If I change the third line to $photo->addChild('file',
'P1270081')->addAttribute('size', '3309519')->addAttribute('type', 'JPG');
I'm getting this error message:
Fatal error: Call to a member function addAttribute() on a non-object in ...
I am new to creating XML files on the fly with SimpleXMLElement so I don't
know how I shall fix this issue. What should I do to fix it?