From: Dennis Edwards <dedward@...>
Date: 2008-06-08T23:28:46+09:00
Subject: Re: rexml & nested loops

I get that part of the syntax -  what I don't (or didn't) get is why
the two xpath operations I have are referring to the same document - I
assumed they would be scoped to only the data passed to the block.





On Jun 8, 2:35 am, Robert Klemme <shortcut...@googlemail.com> wrote:
> On 08.06.2008 00:15, Paul Ash wrote:
>
>
>
> > I'm a bit of a newbie to Ruby, and to xpath..... and hoping someone here
> > can give me the one-liner version of why this is failing.
>
> > I have an XML structure like:
>
> > <foos>
> >     <foo>
> >     <fooID>Foo1</fooID>
> >     <subfoos>
> >         <subfoo>
> >             <subfooName>foobar1</subfooName>
> >         </subfoo>
> >         <subfoo>
> >             <subfooName>foobar2</subfooName>
> >         </subfoo>
> >     </subfoos>
> >     </foo>
> >     <foo>
> >     <fooID>Foo2</fooID>
> >     <subfoos>
> >         <subfoo>
> >             <subfooName>foobar3</subfooName>
> >         </subfoo>
> >         <subfoo>
> >             <subfooName>foobar4</subfooName>
> >         </subfoo>
> >     </subfoos>
> >     </foo>
> > </foos>
>
> > And the code
>
> > doc.each_element('//foo') { |foo|
> >  puts "*** Processing #{foo.elements['fooId'].text}"
> >  foo.each_element('//subFoo') { |subFoo|
> >    puts subFoo.elements["subfooName"].text
> >    }
> >  }
>
> > What I was expecting was a nested loop.. but what I get is:
>
> > doc.each_element('//foo') { |foo|
>
> > This iterator does what I expect.
>
> >  foo.each_element('//subFoo') { |subFoo|
>
> > This iterator seems to give me all instances of subFoo in doc, not just
> > in the current instance of foo.
>
> > I'm sure this i just something about ruby that I don't understand... but
> > can someone point me in the right direction?
>
> No, it's something about XPath that you do not understand. :-)  "//"
> means "from the root of the document", so you are iterating all "subfoo"
> elements each time.  I can think of two remedies:
>
> 1. do a single loop with an XPath expression that selects only "subfoo"
> below "foo"'s.
>
> 2. keep your nested loop but change the XPath expression to not start at
> the root.  (I believe it should be ".//subfoo".)
>
> These are the two pages I usually consult when in doubt about XPath
> expressions:
>
> http://www.w3schools.com/xpath/http://www.zvon.org/xxl/XPathTutorial/General/examples.html
>
> And then there's of course the standard:
>
> http://www.w3.org/TR/xpath
>
> Kind regards
>
>         robert