Node no longer exists using SimpleXML

问题:

Trying to cache an xml file using the build in wordpress function called get_transient but I'm getting a php error:

unserialize() [function.unserialize]: Node no longer exists

//check the db to see if it exists ( get_transient is a WordPress function)
if (false === ($response_xml = get_transient('stats_from_xml_feed'))){

 $request_url = "http://example.com/feed.xml";
 $request_url = urlencode($request_url);
 $response_xml = @simplexml_load_file($request_url);
 //kill request if connection problem
 if ($response_xml === FALSE){
 exit ('could not connect');
 } else {
     // here we throw it into the WordPress temp DB using set_transient for 12 hours
   set_transient('stats_from_xml_feed', $response_xml, 60*60*12);

 //some output
$res =  $response_xml;
$name = $res->name;

echo $name;
}

回答1:

Your $response_xml is an instance of the SimpleXMLElement class. A SimpleXMLElement should not be (un)serialized, because it wraps a resource within the object.

Instead, serialize something which will happily survive the process; the raw response from the feed, all/part of the XML after loading it into the SimpleXMLElement and using the asXML() method, an array of the (likely string) values you want, or some other structure which is okay to be serialized.

One thing to consider is that you will see the unserialize(): Node no longer exists warning in "older" (to use the term loosely) versions of PHP. As of PHP 5.3.2, the behaviour changed to throw an Exception with the message Serialization of 'SimpleXMLElement' is not allowed.

回答2:

You shouldn't (can't?) serialize and unserialize the SimpleXML object. It's XML, which is a serialization format to begin with. This ain't Inception here!

Call the asXML method to get the actual XML, then store that instead.