How to get the absolute node path in XML using XPath and Ruby?

Question

Basically I want to extract the absolute path from a node to root and report it to the console or a file. Below is the current solution:

require "rexml/document"

include REXML

def get_path(xml_doc, key)
  XPath.each(xml_doc, key) do |node|
    puts "\"#{node}\""
    XPath.each(node, '(ancestor::#node)') do |el|
      #  puts  el
    end
  end
end

test_doc = Document.new <<EOF
  <root>
   <level1 key="1" value="B">
     <level2 key="12" value="B" />
     <level2 key="13" value="B" />
   </level1>
  </root>
EOF

get_path test_doc, "//*/[@key='12']"

The issue is that it gives me "<level2 value='B' key='12'/>" as output. Desired output is <root><level1><level2 value='B' key='12'/> (format could be different, the main goal is to have a full path). I have only basic knowledge of XPath and would appreciate any help/guidance where to look and how to achieve this.

Answer 1

If you're set on REXML, here's a REXML solution:

require 'rexml/document'

test_doc = REXML::Document.new <<EOF
  <root>
    <level1 key="1" value="B">
      <level2 key="12" value="B" />
      <level2 key="13" value="B" />
    </level1>
  </root>
EOF

def get_path(xml_doc, key)
  node = REXML::XPath.first( xml_doc, key )
  path = []
  while node.parent
    path << node
    node = node.parent
  end
  path.reverse
end

path = get_path( test_doc, "//*[@key='12']" )
p path.map{ |el| el.name }.join("/")
#=> "root/level1/level2"

Or, if you want to use the same get_path implementation from the other answer, you can monkeypatch REXML to add an ancestors method:

class REXML::Child
  def ancestors
    ancestors = []

    # Presumably you don't want the node included in its list of ancestors
    # If you do, change the following line to    node = self
    node = self.parent

    # Presumably you want to stop at the root node, and not its owning document
    # If you want the document included in the ancestors, change the following
    # line to just    while node
    while node.parent
      ancestors << node
      node = node.parent
    end

    ancestors.reverse
  end
end