Getting specific xml data on php with xpath - php

Question

I have a xml response like that;
<n:Crev xmlns:soap="http://a.com"
xmlns:obj="http://b.com"
xmlns:n="http://c.com"
xmlns:msg="http://d.com"
xmlns="http://e.com"
xmlns:xsi="http://f.com"
xsi:schemaLocation="http://g.com">
<n:Header>
<msg:mydata>123123</msg:mydata>
</n:Header>
</n:Crev>
now I want to get 'msg:mydata' value..
I tried some xpaths but they didn't work and tried online xpath creator it gives something like;
'/n:Crev[#xmlns:soap="http://a.com"]/n:Header/msg:mydata/text()'
but it didn't work also.. So how can I write xpath for that?
Thanks

Answer 1

I've succeeded with following code:
<?php
$xmlStr = '<n:Crev xmlns:soap="http://a.com"
xmlns:obj="http://b.com"
xmlns:n="http://c.com"
xmlns:msg="http://d.com"
xmlns="http://e.com"
xmlns:xsi="http://f.com"
xsi:schemaLocation="http://g.com">
<n:Header>
<msg:mydata>123123</msg:mydata>
</n:Header>
</n:Crev>';
$xmlDoc = new DOMDocument();
$xmlDoc->loadXML($xmlStr);
$xmlPath = new DOMXPath($xmlDoc);
var_dump($xmlPath->query('//n:Crev/n:Header/msg:mydata')->item(0)->textContent);
result:
string '123123' (length=6)

Answer 2

n or msg are namespace prefixes. The actual namespaces are the values of the xmlns attributes. The XML parser will resolve the namespaces.
Here is a small example:
$document = new DOMDocument();
$document->loadXml('<n:Crev xmlns:n="http://c.com"/>');
var_dump(
$document->documentElement->namespaceURI,
$document->documentElement->localName
);
Output:
string(12) "http://c.com"
string(4) "Crev"
The following XMLs all would have the same output:
<n:Crev xmlns:n="http://c.com"/>
<Crev xmlns="http://c.com"/>
<c:Crev xmlns:c="http://c.com"/>
You can read the node as {http://c.com}Crev.
To fetch nodes or scalar values from the DOM you can use Xpath::evaluate(). But to match namespaces you will have to register prefixes for the Xpath expressions. This allows the Xpath engine to resolve the namespaces and match them against the node properties. The prefixes do not have to be the same as in the document.
$xml = <<<'XML'
<n:Crev xmlns:n="http://c.com" xmlns:msg="http://d.com">
<n:Header>
<msg:mydata>123123</msg:mydata>
</n:Header>
</n:Crev>
XML;
$document = new DOMDocument();
$document->loadXml($xml);
$xpath = new DOMXpath($document);
$xpath->registerNamespace('c', 'http://c.com');
$xpath->registerNamespace('msg', 'http://d.com');
var_dump(
$xpath->evaluate('string(/c:Crev/c:Header/msg:mydata)')
);
Output:
string(6) "123123"
If the expression is an location path like /c:Crev/c:Header/msg:mydata the result with be an DOMNodeList, but Xpath functions or operators can return scalar values.