I have a model with an attribute car I want to add a field car_created_at that will have as a value the timestamp of the first time car actually assigned a value. What is the proper way to do that? maybe after_update hook?

CodePudding user response：

According to the trusty rails docs, after_update only runs on updates.

after_save runs both when created and updated. So I would use that.

And beware that just doing save in the hook will cause infinite call stack, meaning save will trigger after_save, in which save is called.

So you will have to use update_columns.

after_save :touch_car_created

def touch_car_created
  if car_created_at.nil?
    update_columns(car_created_at: Time.zone.now)
  end
end

CodePudding user response：

I would prefer to go with before_save because this callback get called before object creation and updation.

# This callback works only when car value has changed
# and car_created_at is nil.
before_save :assign_car_created_time, if: Proc.new { car_changed? && car_created_at.nil? }

private
# Keep it private so it won't be accessed publicly.

def assign_car_created_time
  # We only need to assign the value
  self.car_created_at = Time.zone.now
end

Hope this works for you.