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Re: Extracting values from xml file using php/xpath/namespace/simplexml/

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Denis McMahon wrote:

> On Fri, 05 Sep 2014 04:08:09 +0200, Christoph M. Becker wrote:
>> Jerry Stuckle wrote:
>>> On 9/4/2014 5:21 PM, Thomas 'Pointed Head' Lahn wrote:
>>>> Jerry Stuckle wrote:
>>> His code will detect the change in the markup.  Yours will not, because
>>> you are not using the full XPath.  And once again - yours can fail if
>>> the XML happens to have multiple (but different) XPaths with the same
>>> identifiers.  The Ops will not.
>> 
>> "Mutitple (but different) XPaths"?  Do you mean multiple (but different)
>> XPath expressions?
> 
> No
> 
> Jerry is trying to point out to tpel-troll that if you use a partial xpath
> instead of a fully qualified xpath to match data in an xml document,
> there is a risk that if the same partial xpath matches one or more
> unwanted elements as well as the wanted element(s), the unwanted element
> (s) will end up as part of the selection.

If he would have, this would be showing that he does not understand XPath.
As you assume he did, you clearly do not understand XPath.

An XPath query always matches all elements that match that path.  In a XML 
document

  <foo>
    <bar id="baz" />
    <bar id="bla" />
  </foo>

the path '/foo/bar' matches <bar id="baz" /> *and* <bar id="bla" />.

Therefore, the return value of SimpleXMLElement::xpath() is *always* an 
array, unless the query is syntactically in error, in which case the return 
value is FALSE.

As for “unwanted elements”, it is a fallacy to assume that if the structure 
of the XML document changes, a more general query *must* return unwanted 
elements.  For example, if the structure changes to

  <foo>
    <bars>
      <bar id="baz" />
      <bar id="bla" />
    </bars>
  </foo>

(which makes sense structurally) the result for the more general XPath query 
'.//bar' will still contain only wanted elements, namely still only <bar 
id="baz" /> and <bar id="bla" />.  It could be further refined by using 
/bars[1] as *context node* (using '.' in the path), referring only to nodes 
*below* that node in the hierarchy of the data structure.  This is what I 
referred to with flexibility.  

IOW: Using the full XPath path is _not_ always the best approach.

-- 
PointedEars
Zend Certified PHP Engineer
Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.

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Thread

Extracting values from  xml file using php/xpath/namespace/simplexml/ ofuuzo@gmail.com - 2014-08-13 04:02 -0700
  Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Jerry Stuckle <jstucklex@attglobal.net> - 2014-08-13 09:25 -0400
    Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ ofuuzo@gmail.com - 2014-08-14 03:29 -0700
      Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Jerry Stuckle <jstucklex@attglobal.net> - 2014-08-14 10:06 -0400
      Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-08-17 19:43 +0200
        Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Jerry Stuckle <jstucklex@attglobal.net> - 2014-08-17 15:21 -0400
          Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-08-17 23:41 +0200
            Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Jerry Stuckle <jstucklex@attglobal.net> - 2014-08-17 18:57 -0400
              Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-09-03 23:10 +0200
                Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Jerry Stuckle <jstucklex@attglobal.net> - 2014-09-03 20:11 -0400
                Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-09-04 02:42 +0200
                Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Jerry Stuckle <jstucklex@attglobal.net> - 2014-09-03 21:57 -0400
                Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-09-04 23:21 +0200
                Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Jerry Stuckle <jstucklex@attglobal.net> - 2014-09-04 20:43 -0400
                Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-09-05 04:08 +0200
                Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Denis McMahon <denismfmcmahon@gmail.com> - 2014-09-05 02:50 +0000
                Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Jerry Stuckle <jstucklex@attglobal.net> - 2014-09-05 08:24 -0400
                Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-09-07 11:57 +0200
                Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ Jerry Stuckle <jstucklex@attglobal.net> - 2014-09-07 09:54 -0400
                Re: Extracting values from  xml file using php/xpath/namespace/simplexml/ "M. Strobel" <sorry_no_mail_here@nowhere.dee> - 2014-09-07 23:53 +0200

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