Easy Notification System in Rails Part 3

Read part 1 and part 2 of this series

In this post, we will be sending automatic e-emails every time notifications are created.

Creating the Mailer

We will work with one mailer that will send e-mails for every notification that is created. We can generate our mailer with this command:

rails g mailer NotificationsMailer

Our mailer will contain an action for each notifiable type that works with notifications in our application. In this series, we've been using comments and posts as examples.

Therefore, we can create an action for each:

# app/mailers/notifications_mailer.rb

class NotificationsMailer < ApplicationMailer
  before_action { @notification = params[:notification] }

  default from: 'youremail@yourdomain.com'

  def post_notification
    @recipient = @notification.recipient
    @url = post_url(@notification.notifiable)

    mail(to: @recipient.email, subject: t('email.notifications.subject'))
  end

  def comment_notification
    @recipient = @notification.recipient
    @url = post_url(@notification.notifiable.post)

    mail(to: @recipient.email, subject: t('email.notifications.subject'))
  end

end

Notice that we are using a new Rails 5.1 ActionMailer::Parameterized feature. This allows us to use a before_action to set instance variables before all actions, similar to controllers. These parameters will then be manually passed when the mailer is called.

Mailer Views

Let's go ahead and build the mailer's views. For each mailer action, we must create a HTML view and a plain text view with the same name. Here is an example view for posts mail:

-# app/views/notifications_mailer/post_notification.html.haml

!!!
%html
  %head
    %meta{:content => "text/html; charset=UTF-8", "http-equiv" => "Content-Type"}
  %body
    %p
      %strong #{@notification.actor.full_name}
      = t("notifications.actions.#{@notification.action}")
      a new post titled
      %strong= @notification.notifiable.title

    %p= simple_format h @notification.notifiable.description

    %hr

    = link_to 'View in application', @url

Notice how I am using I18n to localize and internationalize some strings using the t() method in the mailer actions and views. You can discard this and simply enter a hardcoded string if you want.

Sending the E-mails

We will be using again ActiveRecord callbacks on our Notification model to send the e-mail:

# app/models/notification.rb

class Notification < ApplicationRecord
  # ...

  after_create :mail_notification

  private

  def mail_notification
    action = (self.notifiable_type.underscore + '_notification').to_sym

    NotificationMailer.with(notification: self).send(action).deliver_now
  end

end

With the after_create callback, after the notification object is persisted in the database, Raisl will proceed to call the mail_notification method. In this method we will use the notification's notifiable_type attribute to form an underscored string that should match the corresponding action* in the mailer (post_notification, comment_notification, or any other actions added in the future), represented by a Ruby symbol.

Next we proceed to call the mailer to send the e-mail. We use the with method to manually pass in the notification as a parameter, as mentioned before. We then use the Ruby method send to call the corresponding mailer action based on the symbol we constructed.

~> One downside of using an ActiveRecord callback in this situation is that your application will send e-mails for every notification object created in your application. This may be exactly what you want, but this also means that e-mails will also be sent when creating notifications using the Rails console, or when seeding the database with test data.

Other Enhancements

You can also pretty up your HTML emails by using a framework such as Foundation for E-mails

References