Namespacing problem

gistfile1.txt

With a gemfile like this:

source 'https://rubygems.org'
gem 'nokogiri', '~> 1.6.3.1'
....

And a model defined like this

  class Record < ActiveRecord::Base
    def to_pbcore_xml
      xml = '<?xml version="1.0"?><pbcoreDescriptionDocument xmlns="http://www.pbcore.org/PBCore/PBCoreNamespace.html" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.pbcore.org/PBCore/PBCoreNamespace.html" xsi:schemaLocation="http://www.pbcore.org/PBCore/PBCoreNamespace.html"></pbcoreDescriptionDocument>'
      Nokogiri::XML(xml)
    end
  end
  
I'm getting an error like this

NameError in RecordsController#show
uninitialized constant Record::Nokogiri

Extracted source (around line #22):
  def to_pbcore_xml
    xml = '<?xml version="1.0"?><pbcoreDescriptionDocument xmlns="http://www.pbcore.org/PBCore/PBCoreNamespace.html" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.pbcore.org/PBCore/PBCoreNamespace.html" xsi:schemaLocation="http://www.pbcore.org/PBCore/PBCoreNamespace.html"></pbcoreDescriptionDocument>'
    Nokogiri::XML(xml)
  end
end