From: Paul Battley <pbattley@...>
Date: 2006-08-02T17:45:20+09:00
Subject: Re: REXML XPath: bug or misunderstanding?

On 02/08/06, Robert Klemme <shortcutter@googlemail.com> wrote:> Eric Armstrong wrote:> > ...> > According to the XPath doc, the first argument> > is the "context" element.> >> > So what /should/ happen is that search> > for td elements occurs in the subtree> > rooted at the tbl element, using the> > //td path --which I take to mean "anywhere> > within the context".> >> > But what actually happens is that the> > search for td elements occurs in the> > entire document, so the code above returns> > the first table, regardless of where the> > matching data is found.>> That sounds like a bug.
That's what I thought when I first encountered it, but after lookinginto it in more detail I concluded that it follows the specification.The receiving element does indeed provide context, but using //overrides it: // means the root node or any of its descendants.
> > The workaround is to dispense with the> > outer loop. Once matching data is found> > and keep visiting parents until the> > table ancestor is found. (That patch> > simplifies the code, actually.)>> IMHO the proper solution is to craft a single XPath expression that will> cover your requirement, i.e. any "td" somewhere below a "table".
In general, that is indeed likely to be the best solution. However,just to clear things up, here's how the original poster could havedone what he wanted: use "descendant::td". Here's an example:
  xml = %{    <a>      <b>        <c>          <d id="foo" />        </c>      </b>      <d id="bar" />    </a>  }
  doc = REXML::Document.new(xml)
  REXML::XPath.each(doc, '//b') do |b|    REXML::XPath.each(b, 'descendant::d') do |d|      puts(d.to_s)    end  end
# => <d id='foo'/​>
For comparison:
  REXML::XPath.each(doc, '//b') do |b|    REXML::XPath.each(b, '//d') do |d|      puts(d.to_s)    end  end
# => <d id='foo'/​># => <d id='bar'/​>
Regards,Paul.