example of parsing large xml files in ruby using ox, define a handler, look up for a particular root element

ox_parsing.rb

require "awesome_print"

module XmlParsing
  require "ox"

  class Reader < ::Ox::Sax
    def initialize file_path, target, target_handler
      @target_handler = target_handler
      @target = target
      @file_path = file_path
      @elements = []
    end

    def count
      @count ||= `grep "<#{@target}>" #{@file_path} -o | wc -l`.to_s.strip.to_i
      @count = `grep "<#{@target}" #{@file_path} -o | wc -l`.to_s.strip.to_i if @count==0
      @count
    end

    def parse
      xmlio = IO.new(IO.sysopen @file_path)
      Ox.sax_parse self, xmlio
    end

    def start_element(name)
      name = name.to_s.strip
      @elements.push({ name=>{} })
    end

    def end_element(name)
      name = name.to_s.strip

      if @elements.last[name]
        @element = @elements.pop

        @element.delete name

        if @element.keys.count==1 and @element[:text]
          inject_into_last name, @element[:text]
        else
          inject_into_last name, @element
        end
      end

      @target_handler.next_element @element if @target==name
    end

    def inject_into_last name, value
      return unless @elements.last
      
      if @elements.last[name]
        @elements.last[name] = [ @elements.last[name] ] unless @elements.last[name].is_a? Array
        @elements.last[name].push value

      else
        @elements.last[name] = value
      end
    end

    def attr(name, value)
      return unless @elements.last

      name = name.to_s.strip
      value = value.to_s.strip

      @elements.last[:attrs] ||= {}
      @elements.last[:attrs][name] = value
    end

    def text(value)
      return unless @elements.last
      value = value.to_s.strip
      @elements.last[:text] = value
    end
  end
end

module XMLPropertiesHandler
  class Premthus
    def next_element property
      ap property
      exit
    end
  end
end

XmlParsing::Reader.new("mits.xml", "Property", XMLPropertiesHandler::Premthus.new).parse




#
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# below one is a nokogiri example which is trying easiest way to deal with nokogiri sax parsing
# http://amolnpujari.wordpress.com/2012/03/31/reading_huge_xml-rb/
#
#