XML : Need to use a XML from internet in a ruby on rails application?

I am using rails 4 and need to use data from a link which is in xml format. I searched about it and found nokogiri is the best. So, I followed this- http://code.runnable.com/UjQ4mOziD5kVAAFD/nokogiri-html-parser-example-for-ruby-on-rails

And used

  require 'open-uri'    

at the top of my controller and used gem 'nokogiri' , but then too it's throwing an error of Uninitialized Nokogir::nokogiricontroller.

Please suggest me the best way to use the data from an xml format.