How does after_save work when saving an object

Question

If I do the following:

@user.name = "John"    
@user.url = "www.john.com"
@user.save

If I use after_save

@user.url = "www.johnseena.com"
@user.save

What will happen when I do this?

I believe it should save the value because of the 'after_save' callback.

Answer 1

In my opinion, if you call save function in a after_save callback, then it will trap into a recursion unless you put a guard at the beginning. like this

class User < AR::Base
      after_save :change_url

      def change_url
          #Check some condition to skip saving
          url = "www.johnseena.com"
          save              #<======= this save will fire the after_save again
      end
end

However, apart from putting a guard, you can use update_column also

def change_url
    update_column(:url, "www.johnseena.com")
end

In this case it will not fire after_save. However, it will fire after_update. So if you have any update operation on that call back then you are in recursion again :)

Answer 2

The after_save callback will be triggered irrespective its a save or an update on that object.

Also,

update_column doesn't trigger any callbacks(ie after_update) and skips validations too. see http://apidock.com/rails/ActiveRecord/Persistence/update_column

U should specifically use after_create or after_update depending upon the operation and its timing.

after_create :send_mail
def send_x_mail
  #some mail that user has been created
end

after_update :send_y_mail
def send_y_mail
  #some data has been updated
end

after_save :update_some_date
def update_some_data
  ...
  action which doesnt update the current object else will trigger the call_back
end

Also see What is the difference between `after_create` and `after_save` and when to use which? and for callbacks see http://ar.rubyonrails.org/classes/ActiveRecord/Callbacks.html#M000059