Ruby-on-rails – How to determine if a record is just created or updated in after_save

activemodelactiverecordruby-on-rails

The #new_record? function determines if a record has been saved. But it is always false in the after_save hook. Is there a way to determine whether the record is a newly created record or an old one from update?

I'm hoping not to use another callback such as before_create to set a flag in the model or require another query into the db.

Any advice is appreciated.

Edit: Need to determine it in after_save hook, and for my particular use case, there is no updated_at or updated_on timestamp

Best Answer

I was looking to use this for an after_save callback.

A simpler solution is to use id_changed? (since it won't change on update) or even created_at_changed? if timestamp columns are present.

Update: As @mitsy points out, if this check is needed outside of callbacks then use id_previously_changed?. See docs.

Rails 5.1+

Use saved_change_to_published?:

class SomeModel < ActiveRecord::Base
  after_update :send_notification_after_change

  def send_notification_after_change
    Notification.send(…) if (saved_change_to_published? && self.published == true)
  end

end

Or if you prefer, saved_change_to_attribute?(:published).

Rails 3–5.1

Warning

This approach works through Rails 5.1 (but is deprecated in 5.1 and has breaking changes in 5.2). You can read about the change in this pull request.

In your after_update filter on the model you can use _changed? accessor. So for example:

class SomeModel < ActiveRecord::Base
  after_update :send_notification_after_change

  def send_notification_after_change
    Notification.send(...) if (self.published_changed? && self.published == true)
  end

end

It just works.

Ruby-on-rails – Rails – ActiveRecord – Trigger mail on change of a field value

1) might be a little subjective but I'll answer that along with 2) ActiveRecord provides methods to indicate whether an attribute has changed. You can use the attribute name + _changed?. E.g. If your model has a name attribute, then it will also respond to #name_changed? Here is one way you can send email only if an attribute has been changed:

class MyModel
  after_update :send_email, :if => :column_name_changed?

  def send_email
    # Send email here
  end
end

3) The old attribute value can be accessed by appending _was. E.g. #name_was will return the old value of the name field.

UPDATE:

To send an email only the first time that a field is switched from false to true you will need to add another field to your database, such as email_sent. Since the condition for the send_email callback became more complex, I moved it into the callback itself. After the email is sent, set the email_sent field to true, so that no further emails are delivered.

class MyModel
  after_update :send_email

  def send_email
    if column_name_changed? && !email_sent?
      # Send email here
      update_attribute :email_sent, true
    end
  end
end

Best Answer

Related Solutions

Ruby-on-rails – Determine what attributes were changed in Rails after_save callback

Rails 5.1+

Rails 3–5.1

Warning

Ruby-on-rails – Rails – ActiveRecord – Trigger mail on change of a field value

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