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

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On 8/17/2014 5:41 PM, Thomas 'PointedEars' Lahn wrote:
> Jerry Stuckle wrote:
> 
>> On 8/17/2014 1:43 PM, Thomas 'PointedEars' Lahn wrote:
>>> You do not have to register namespaces that you do not use in your XPath
>>> query.  See below.
>>
>> It doesn't hurt - and if he wants to use them in the future, he's
>> already got it.  I often register namespaces I don't need *immediately*.
> 
> Premature "optimization"…
>

No, it is not optimization.  It is planning for future enhancements (and
possible reusability).  Good design means planning for such - not that
YOU would know.

>>>> $xpath->registerNamespace('dc', 'http://purl.org/dc/elements/1.1/');
>>>>
>>>> $records = $xpath->evaluate('/oai:OAI-PMH/oai:ListRecords/oai:record',
>>>> NULL, FALSE); foreach ($records as $entry) {
>>>>   // […]
>>>>   $dc = $xpath->evaluate('oai:metadata/oai-dc:dc/dc:*', $entry, FALSE);
>>>>   foreach ($dc as $dcElement){
>>>>     switch ($dcElement->localName) {
>>>>     case 'title' :
>>>>       echo 'Title: '.$dcElement->nodeValue;
>>>>       echo "\n";
>>>>       break;
>>>>     case 'date' :
>>>>       echo 'Date: '.$dcElement->nodeValue;
>>>>       echo "\n";
>>>>       break;
>>>>     case 'relation' :
>>>>       echo 'Relation: '.$dcElement->nodeValue;
>>>>       echo "\n";
>>>>       break;
>>>>
>>>>     }
>>>>   }
>>>> }
>>>> ?>
>>>
>>> You do not have to specify the whole path with XPath if you are certain
>>> of uniqueness (or content with iteration over content-duplicates is
>>> acceptable), and you certainly do not have to iterate over elements to
>>> find
>>> matches.  All of this is built into XPath, see the XPath 1.0
>>> Specification [0], particularly the “Location Paths” section.
>>
>> Again, it's a good idea to specify the whole path.
> 
> No, it is not.  It makes the code very inflexible at no advantage.  For 
> example, no elements will be found if the full path is specified and the 
> namespace prefix or the namespace URI changes.  Of course, if the prefix is 
> not allowed to change you can find out the URI by reading the namespace 
> attribute, but it would still be an unnecessary step because the pertaining 
> elements are not of interest here.
> 

And the wrong path will be found if the elements are not unique.  If you
specify the whole path and it is not found, you will get an error.  If
you have a non-unique path, you will get very hard to find bugs.

>> Unless he created the XML file, he can't ensure that it will be unique. 
> 
> It is not possible to apply XPath to a document whose basic structure is 
> unknown in any case, so that is a specious argument.
> 

He knows the current structure of the document.  He does not know the
future structure - which is *exactly why he should specify the whole path*.

> If the target elements are not unique, but exist pair-wise per “record” 
> element (which can be assumed here), the result will be the same because 
> SimpleXMLElement::xpath() always returns an array.
> 

No, the results will only be the same if the values are the same.  If
they are not, he could easily pick up incorrect values - and spend hours
trying to debug the problem.

> However, if that cannot be guaranteed or not only the first match is of 
> interest, then the best (shortest, most efficient) approach is to first find 
> the ancestors that are not unique, and then use them as context nodes:
> 
>   foreach ($xml->xpath('./ListRecords/record') as $record)
>   {
>     $title = $record->xpath('.//dc:title')[0];
>     $date  = $record->xpath('.//dc:date')[0];
> 
>     /* do something with $title and $date */
>   }
> 

Only if he knows the path he wants.

> It certainly is _not_ to reinvent the wheel^WXPath query engine like the OP 
> did.
> 

He did not "reinvent the wheel".  He processed the data correctly.

>> As for iterating over the elements - it's not uncommon to do it that way. 
> 
> It is uncommon to do it the way of the OP among those who know both XPath 
> and the DOM well.
> 

Only in your mind.

>> Otherwise you have to check to ensure each element exists before using it. 
> 
> No, one does not have to.  That’s the beauty of it.
> 

And what do you do when an element doesn't exist?  You have to test each
element you're looking at.

>> By iterating, you can set default values and change those which exist.
> 
> One can do that anyway.
>  

Yes, oh great moron?

>> Of course, if you have 100 elements and are only interested in 2-3 of
>> them, this is way inefficient.  However, if you have 5 elements and want
>> all of them, it can be more efficient and is definitely shorter.
> 
> The proof is in the pudding.  My first suggestion had 4 statements in 5 
> lines.  My new suggestion has 3 statements in 7 lines, not counting the 
> instantiation and namespace registration.  How many had the OP’s?  How many 
> would it have if rewritten to use SimpleXMLElement but keeping the same 
> approach?
>  

And both of your suggestions will fail in many instances - like with
non-unique elements.  The op's will not.

>>> Here it is with SimpleXMLElement, which you can apply to your DOMDocument
>>> approach, too:
>>>
>>> <?php
>>>   $xml = new SimpleXMLElement('tmp/test-oai.xml', 0, true);
>>>   $xml->registerXPathNamespace('dc', 'http://purl.org/dc/elements/1.1/');
>>>   echo $xml->xpath('.//dc:title')[0] . PHP_EOL;
>>>   echo $xml->xpath('.//dc:date')[0] . PHP_EOL;
>>
>> Which will give an E_NOTICE if the path does not exist.
> 
> You mean it would issue “PHP Notice: Undefined offset: 0”?  Yes.  But that 
> would not appear in production because the recommended production setting 
> includes “& ~E_NOTICE”; whereas E_NOTICE is an error constant, not a message 
> type.
>  

And the notice is NOT good.  It indicates a potential bug in the code.
That's why E_NOTICE is issued.  But once again you don't understand good
coding practices.  You think that just because a message can be
suppressed it's not a potential problem.

> The result of the array element access would be “null”, where the suggested 
> defaults could take effect:
> 
>   $title = ($record->xpath('.//dc:title')[0] ?: '(unknown)');
>   $date  = ($record->xpath('.//dc:date')[0]  ?: '(unknown)');
> 

And gives the E_NOTICE, which you conveniently ignore.

>> To the OP:
>>
>> Better yet […] post just like you did before.  There was nothing wrong
>> with your post.
> 
> I have stated what was wrong.  It is there for all to see.  Why do you want 
> to mislead them?  And why do you think name-calling is going to achieve 
> that?
> 

You are a pedantic troll, as you have once again proven (and are known
in multiple newsgroups).  And you again proved you know nothing about
good coding practices (as you have also proven in multiple newsgroups).

-- 
==================
Remove the "x" from my email address
Jerry Stuckle
jstucklex@attglobal.net
==================

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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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