gistfile1.rb

# PaperTrail's version class (existing code omitted for clarity).
class Version < ActiveRecord::Base
  before_update :before_update_hook
  after_update :after_update_hook

  def before_update_hook
  end

  def after_update_hook
  end
end

# In a client Rails app, re-open version class to implement hooks.
class Version < ActiveRecord::Base
  def before_update_hook
    self.phase_of_moon = MoonWebService.get_phase
  end
end