Re: [xml] How to select a node based on attribute values?

[Yan Seiner <yan seiner com>]

John Dennis wrote:

> On Tue, 2006-11-28 at 16:57 -0800, Yan Seiner wrote:
>
> > Fist off, I'm a total newbie when it comes to libxml.  I've been able to 
> > work my way through some examples, and produce working code, but I'm not 
> > entirely happy with the result, and I would like some advice.
> >
> > I have an XML tree that looks like this:
> >
> > <root>
> >    <plc id="1">
> >       <some stuff/>
> >    </plc>
> >    <plc id="2">
> >       <some other stuff/>
> >    </plc>
> > </root>
> >
> > I have a relatively small number (< 50) of the plc nodes, but the whole 
> > tree is pretty big.
> >
> > What is the best (or simplest way) to retrieve the information for plc 2?
> >    
>  
>
> xpath is the simplest and most powerful
>
> > Should I pull all of the plc elements using xmlXPathEvalExpression, and 
> > then iterate over them with xmlGetProp looking for an id attribute with 
> > a value of "2"?
> >    
>
> no need to iterate, just create an xpath expression which specifies id=2
>
> off the top of my head the expression would be "/plc[ id="2"]"
>
> just google xpath syntax or xpath examples, you'll turn up a ton

OK, thanks a lot for the above!

I'm working with an embedded platform, so it took me a bit to get all of 
the required libxml stuff together and rebuild PHP with libxml support....

Now I have xpath working with PHP.   Yaay!

Ok, now for the PHP + xml question:

I am trying to get the base node of a schedule; I've attached a small 
portion of my XML file below.  What I would like to do is to get the 
root of a schedule, and then iterate with foreach through all of the 
children.  This is the function I came up with and of course it doesn't 
work.  I don't understand how I am supposed to work with the object that 
the xpath_eval[_expression] returns.  I've also tried the child_nodes 
method and that fails as well.

Hopefully there is a PHP expert on the list who can shed some light on this.

Thanks,

--Yan

   function loadSchedule($pivotID, $schedName, $schedNum) {
   $dom = domxml_open_file("/tmp/test.conf");
   $xpath = xpath_new_context($dom);
   // find base node for our schedule
   $pat = '//root/pivot[ id="' . $pivotID . '"]/'
       . $schedName . '[ id="' . $schedNum . '"]';
   print $pat;
   $baseNode = xpath_eval($xpath,$pat);
   var_dump($baseNode);
   $lines = xpath_eval_expression($xpath,'/line',$baseNode);
   var_dump($lines);
   print "\nOK\n";
   foreach($lines->nodeset as $line) {
       var_dump($line);
       }
   }

<root>
   <pivot id="1">
       <water id="1">
           <line id="1">
               <bearingTo>120.0</bearingTo>
               <WetDry>1</WetDry>
               <FwdRev>0</FwdRev>
               <event>0</event>
               <speed>10</speed>
           </line>
           <line id="2">
               <bearingTo>180.0</bearingTo>
               <WetDry>1</WetDry>
               <FwdRev>1</FwdRev>
               <event>0</event>
               <speed>45</speed>
           </line>
       </water>
   <pivot>
</root>