module ActiveRecord::Timestamp

product.touch(:designed_at) # updates the designed_at attribute
product.touch # updates updated_at

Examples:

If an attribute name is passed, that attribute is used for the touch instead of the updated_at/on attributes.
If the save fails because of validation errors, an ActiveRecord::RecordInvalid exception is raised.
Saves the record with the updated_at/on attributes set to the current time.

def touch(attribute = nil)
  current_time = current_time_from_proper_timezone
  if attribute
    write_attribute(attribute, current_time)
  else
    write_attribute('updated_at', current_time) if respond_to?(:updated_at)
    write_attribute('updated_on', current_time) if respond_to?(:updated_on)
  end
  save!
end