Rails attribute changed callback

This week, I’d like to show you how to do an action, when an Active Record model’s attribute changes.

In the example, we have a User model, and we want to send an email to the user when the verified attribute changes to true.

As a first step, we need to add an after_save callback to the model:

# app/models/user.rb

class User < ApplicationRecord

  after_save :send_verified_email_if_needed

  def send_verified_email_if_needed

  end

end

In the second step, we will use the ActiveModel::Dirty module of Rails. This module is included by default in all Active Record models, and it provides methods around attibute changes. The method we need this time is attribute_changed?(attribute). But we will use verified_changed?, which is a shorthand version, to determine when the attribute changed:

# app/models/user.rb

class User < ApplicationRecord

  after_save :send_verified_email_if_needed

  def send_verified_email_if_needed

    if verified_changed? && verified

      UserMailer.with(user: self).confirmed.deliver

    end

  end

end

We also check that the attribute is true and we send the email if the conditions meet.

That’s it for this time.