get the value of the <doc> xml element to use in query - php

Question

I have this code
$xml = $mbpay->processPaymentInfo();
Log::info('Showing $mbpay:' . var_export($xml, true));
The log shows like:
[2018-07-06 12:40:56] local.INFO: Showing $mbpay: '<?xml version="1.0" encoding="ISO-8859-1" ?>
<getmb_id>
<status>ok</status>
<!---->
<doc>000...</doc>
</getmb_id>'
With this xml, I want to get from the notifications table the value of the column "r_id" where the value of the "doc" column is equal to the "doc" element of the $xml above.
Do you know how to properly get the value of the xml element so is possible to do the query to get the r_id?
The query should be something like " $rID = Notifications::where('doc', $doc)->pluck('r_id')->first();
" but how to get the $doc?
updated:
$mbpay = new MBPay($payment_info);
$processed_payment = $mbpay->processPaymentInfo();
$xml = simplexml_load_string($processed_payment);
$doc = $xml->doc;
$rID = DB::table('notifications')->where('doc', $doc)->pluck('r_id')->first();
Log::info('Showing $mbpay: ' . var_export($xml, true));
Log::info('doc: ' . var_export($doc, true)); // shows SimpleXMLElement::__set_state(array(
))
Log::info('rID: ' . var_export($rID, true)); // shows NULL
Log::info('xml: ' . var_export($xml, true));
return \Response::make($xml, '200')->header('Content-Type', 'text/xml');
The $mbpay->processPaymentInfo() shows like:
<?xml version="1.0" encoding="ISO-8859-1" ?>
<getmb_key>
<status>ok</status>
<message>...</message>
<user>...</user>
<doc>...</doc>
</getmb_key>

Answer 1

Assuming you will only ever expect one doc node, there are a few ways you can go about getting the value of the node. The first thing that comes to mind is simplexml_load_string():
$processed_payment = $mbpay->processPaymentInfo();
$xml = simplexml_load_string($processed_payment);
$doc = (string) $xml->doc;
We can also parse it with DOMDocument's loadXML():
$dom = new \DOMDocument();
$dom->loadXML($processed_payment);
$docs = $dom->getElementsByTagName('doc');
$doc = $docs->item(0)->nodeValue;
As well as with SimpleXMLElement::
$element = new \SimpleXMLElement($processed_payment);
$doc = (string) $element->doc[0];
Finally, there's good old regex with preg_match:
$result = preg_match("/<doc>(.*?)<\\/doc>/", $processed_payment, $matches);
var_dump($matches[1]);
Which method you use depends on the structure of your document and, somewhat, your personal preference. For me, simplexml_load_string() was the first thing that came to mind, but after considering alternatives and given the knowledge of the expected structure, I think I'd prefer SimpleXMLElement().
Here are working examples of each method above.