URL shortening in ruby : http://proccli.com/url-shortening-ruby-rails

active_record_url_shortening.rb

# You can use the model's ID (PK/Serial) to generate a token which can be reversed:
# Example:
#   Url.find(7213).shortened        #=> 5kd
#   Url.find_by_shortened("5kd")    #=> #<Url id: 7213...>
class Url < ActiveRecord::Base
  Radix = 36
  
  # convert ID into a shortened version
  def shortened
    id.to_s(Radix)
  end

  # unconvert the shortened version back to an ID
  def self.shortened_to_id(shortened)
    shortened.to_i(Radix)
  end

  # convert and lookup
  def self.find_by_shortened(shortened)
    find shortened_to_id(shortened)
  end
end

short_url_token.rb

# make tinyurl-ish tokens for pages so you dont have a goofy MD5 running amuck 
# Example:
#   make_token  #=> "32uelywr"
# NOTE: the longer the number, the longer the token
def make_token
  ("%d%d" % [rand(100), Time.now.to_i]).to_i.to_s(36)
end