duanpi2033
duanpi2033
2012-03-29 03:19

PHP:如何检查节点是否存在以及是否使用xpath?

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I'm querying Alexa to get a given url's ranking. The return is in XML. Most times Alexa returns XML containing the REACH & RANK values, though sometimes it doesn't. When it doesn't, the code below that grabs the value for RANK throws an error:

Fatal error: Call to a member function xpath() on a non-object...

// Alexa Ranking
$url = 'http://data.alexa.com/data?cli=10&dat=s&url=' . $final_site;
$ch = curl_init(); // initialize curl handle
curl_setopt($ch, CURLOPT_URL,$url); // set url to post to
curl_setopt($ch, CURLOPT_RETURNTRANSFER,1); // return into a variable
curl_setopt($ch, CURLOPT_TIMEOUT, 4); // times out after 4s
$result = curl_exec($ch); // run the whole process
$xml = simplexml_load_string($result);
//Get reach node
$popularity = $xml->xpath("//REACH"); // <-- ERROR OCCURS HERE
//Get the rank attribute
$alexa_rank = (string)$popularity[0]['RANK'];

Like I mentioned above, sometimes the xml tree looks like:

<ALEXA VER="0.9" URL="venturengine.com/" HOME="0" AID="=">
<SD TITLE="A" FLAGS="" HOST="venturengine.com">
<LINKSIN NUM="8"/>
</SD>
<SD>
<POPULARITY URL="venturengine.com/" TEXT="8709770"/>
<REACH RANK="8474566"/>
</SD>
</ALEXA>

and sometimes it looks like:

<ALEXA VER="0.9" URL="store.guldfors.nu/" HOME="0" AID="=">
<SD TITLE="A" FLAGS="" HOST="store.guldfors.nu"></SD>
</ALEXA>

which doesn't have the REACH or RANK nodes/attributes.

Is there anyway to wrap the xpath such as:

if($xml->xpath("//REACH") === TRUE) {
  //Get reach node
  $popularity = $xml->xpath("//REACH"); // <-- ERROR OCCURS HERE
  //Get the rank attribute
  $alexa_rank = (string)$popularity[0]['RANK'];
}

I've tried the above, doesn't work.

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1条回答

  • duan6301 duan6301 9年前

    I'm not sure of the exact syntax, but you might try counting the number of nodes in the target node set and seeing if it's greater than zero.

    For example, count(//Reach) > 0

    Another option appears to be to use boolean(//Reach)

    See xpath find if node exists

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