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Bug #41663 Xpath evaluation in SimpleXMLElement
Submitted: 2007-06-12 08:10 UTC Modified: 2007-06-12 13:18 UTC
From: kenashkov at gmail dot com Assigned:
Status: Not a bug Package: SimpleXML related
PHP Version: 5.2.3 OS: Fedora Core 4
Private report: No CVE-ID: None
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 [2007-06-12 08:10 UTC] kenashkov at gmail dot com
Description:
------------
The evaluation of the Xpath expressions is not relative to the node against which they are called ([2]). Worse - even after cloning a node from the structure and evaluating the xpath, the xpath expression seems to be evaluated against the original structure, not against the new one (which is a copy of a part of the original) ([3]).

This was discussed in the dev-list here:
http://marc.info/?l=php-dev&m=118001203709813&w=2

If this is not a bug, but expected result, I think a note addressing this behaviour must be added in the docs.

Reproduce code:
---------------
$str = '<rootnode><level1_node1><level2_node1></level2_node1></level1_node1><level1_node2></level1_node2></rootnode>';
$x = new SimpleXMLElement($str);

//[1]
$r1 = $x->xpath('/*');
print $r1[0]->getName().' ';

//[2]
$r2 = $x->level1_node1[0]->xpath('/*');
print $r2[0]->getName().' ';

//[3]
$z = clone $x->level1_node1[0];
$r3 = $z->xpath('/*');
print $r3[0]->getName().' ';



Expected result:
----------------
rootnode level1_node1 level1_node1

Actual result:
--------------
rootnode rootnode rootnode

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 [2007-06-12 12:44 UTC] rrichards@php.net
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

The results are exactly what you requested based on your XPath expression. You used absolute paths not relative:
http://www.w3.org/TR/xpath#location-paths
 [2007-06-12 12:50 UTC] kenashkov at gmail dot com
Yes - I use absolute expression. But at least in the last example [3]:
$z = clone $x->level1_node1[0];
$r3 = $z->xpath('/*');
print $r3[0]->getName().' ';

I use the $z object - not the x. And the $z object does not has any node called rootnode. The expression is again evaluated against the $x structure, not the $z.
This could be a problem in the case:

$z = clone $x->level1_node1[0];
function do_something($z)
{
$z->xpath('/*');//some absolute expression
}

Where the function do_something is totally unaware of the existance of the $x var. If this is still expected then how one can evaluate an absolute xpath expression inside the do_something function, as it will always do it for the $x structure, not the locally available $z structure.
I think at least this must be documented and a workaround must be provide in the docs.
 [2007-06-12 13:08 UTC] rrichards@php.net
Still incorrect:
The cloned node is still part of the document (just not linked in).
Using / causes expression to be evaluated against the document.
/* will select the top level element in the same document as the context node

Use ./ to evaluate against and in scope of context node

Note: There was a bug in earlier versions of SimpleXML (pre 5.2 I believe) where the relative path didn't work correctly against the context.
 [2007-06-12 13:18 UTC] kenashkov at gmail dot com
Yes, I experienced strange behaviour with the relative path (exactly in a function - like the example I gave) and this is why I gave now the example with absolute path.
I just expected clone to get the node out of the structure.
Case closed.
 
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