threaded_user.rb

# base_controller.rb

before_filter :set_current_user

def set_current_user
  User.current_user = current_user
end


# user.rb

def self.current_user=(user)
  Thread.current[:current_user] = user
end

def self.current_user
  Thread.current[:current_user]
end

# order.rb

event :complete do
transitions from: :processing, to: :completed,
            after: Proc.new { self.completed_at = Time.now.utc },
            on_transition: Proc.new { self.moved_to_completed_by = User.current_user }
end