XPath-REXML-Ruby: Selecting multiple siblings/ancestors/descendants

Question

This is my first post here. I have just started working with Ruby and am using REXML for some XML handling. I present a small sample of my xml file here:

  <record>
     <header>
        <identifier>oai:lcoa1.loc.gov:loc.gmd/g3195.ct000379</identifier>
        <datestamp>2004-08-13T15:32:50Z</datestamp>
        <setSpec>gmd</setSpec>
     </header>
     <metadata>
           <titleInfo>
              <title>Meet-konstige vertoning van de grote en merk-waardige zons-verduistering</title>
           </titleInfo>
     </metadata>
  </record>

My objective is to match the last numerical value in the tag with a list of values that I have from an array. I have achieved this with the following code snippet:

ids = XPath.match(xmldoc, "//identifier[text()='oai:lcoa1.loc.gov:loc.gmd/"+mapid+"']")

Having got a particular identifier that I wish to investigate, now I want to go back to and select and then select to get the value in the node for that particular identifier.

I have looked at the XPath tutorials and expressions and many of the related questions on this website as well and learnt about axes and the different concepts such as ancestor/following sibling etc. However, I am really confused and cannot figure this out easily.

I was wondering if I could get any help or if someone could point me towards an online resource "easy" to read.

Thank you.

UPDATE:

I have been trying various combinations of code such as:

idss = XPath.match(xmldoc, "//identifier[text()='oai:lcoa1.loc.gov:loc.gmd/"+mapid+"']/parent::header/following-sibling::metadata/child::mods/child::titleInfo/child::title")

The code compiles but does not output anything. I am wondering what I am doing so wrong.

Your sample XML has an extra header. Is that intended? – joelparkerhenderson Apr 06 '12 at 14:35 — joelparkerhenderson, Apr 06 '12 at 14:35
Oops. That was my mistake. Fixed. :) – Shion Apr 06 '12 at 22:22 — Shion, Apr 06 '12 at 22:22

score 1 · Accepted Answer · answered Apr 06 '12 at 14:53

1

Here's a way to accomplish it using XPath, then going up to the record, then XPath to get the title:

require 'rexml/document'
include REXML

xml=<<END
  <record>
    <header>
      <identifier>oai:lcoa1.loc.gov:loc.gmd/g3195.ct000379</identifier>
      <datestamp>2004-08-13T15:32:50Z</datestamp>
      <setSpec>gmd</setSpec>
    </header>
    <metadata>
      <titleInfo>
        <title>Meet-konstige</title>
      </titleInfo>
    </metadata>
  </record>
END

doc=Document.new(xml)
mapid = "ct000379"
text = "oai:lcoa1.loc.gov:loc.gmd/g3195.#{mapid}"

identifier_nodes = XPath.match(doc, "//identifier[text()='#{text}']")
record_node = identifier_nodes.first.parent.parent
record_node.elements['metadata/titleInfo/title'].text
=> "Meet-konstig"

answered Apr 06 '12 at 14:53

joelparkerhenderson

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I tried your solution. It works in the irb. However, when I try to implement it in my code file it returns this error: `dirit.rb:91:in `
': undefined method `text' for nil:NilClass (NoMethodError)` I wonder what I am doing wrong here. I use the text method throughout the program.
– Shion Apr 06 '12 at 22:12
Perhaps you have a typo somewhere in your code? Try cut/paste of my code into a file and run it that way, see if it works. Also be sure you have a period before the mapId. And upvote this answer. :) – joelparkerhenderson Apr 06 '12 at 22:26
Thank you for your suggestions. I had neglected to look at my actual xml file which has a slightly more complicated structure. It works now. I accepted your answer and tried to upvote it but it seems that I do not have the minimum 15 reputation. I promise to come back and upvote when I have that. – Shion Apr 06 '12 at 22:41
Upvoted as promised since I now have the minimum 15 reputation. – Shion Apr 07 '12 at 16:41

XPath-REXML-Ruby: Selecting multiple siblings/ancestors/descendants

1 Answers1