gistfile1.rb

class Invitation < ActiveRecord::Base
  # Returns encoded invitation id
  def encoded_id
    self.id*10011981 * 1820062 - 1981
  end

  def self.decode_id(id)
    i = ((id.to_i + 1981)/1820062)/10011981
    if (i*10011981 * 1820062 - 1981)==id.to_i
      begin
        Invitation.find(i).id
      rescue
        false
      end
    else
      false
    end
  end
end