quick hack at a doman specific url shortner, decided to go a different route but going to gist it incase I want to come back to it

roberto_url_controller.rb

# A Roberto Url is a tiny url.  It depends on the cross-language hashids lib http://www.hashids.org/
class RobertoUrlController < ApplicationController
  layout false
  # cursory glance at the code, this appears to be threadsafe
  HASHER = ::Hashids.new("no offense rob, this is a tribute to your carb intake not your manhood") #change the salt and all urls are invalid!
  PREFIX = "#{Rails.configuration.base_url}/l"
  
  # note, extremely important that you do not change the keys of the object map as the
  # hashing is tied to the sequence key:  So add class maps to the end of the list!
  # also, because classes can be models, use the string representation of the class
  # otherwise the AR connection pool is going to have a fit with threads!
  OBJ_MAP = {
    1 => 'User::Invitation'
  }
  # setup 2 way map
  OBJ_MAP.merge!(OBJ_MAP.invert)
  
  class << self
 
    def model_to_url(model)
      index = OBJ_MAP[model.class.to_s]
      raise "#{model.class.to_s} not mapped to a RobertoUrl" if index.nil?
      "#{PREFIX}#{HASHER.encrypt(index,model.id)}"
    end

    def model_from_id(id)
      index, id = HASHER.decrypt(id)
      OBJ_MAP[index].constantize.find(id)
    end

  end

  def show
    @model = self.class.model_from_id(params[:id])
    if @model.is_a?(User::Invitation)
      return show_user_invitation
    end
  end

  def show_user_invitation
    @invitation = @model
    @invitation_data = {
      id: @invitation.id
    }
    #render :json => @model
    render :action => :user_invitation
  end

end