[Beginning Rails 6] Listing 13-5. sending "comment added" mailer asynchronously

comment.rb

class Comment < ApplicationRecord
  belongs_to :article

  validates :name, :email, :body, presence: true
  validate :article_should_be_published

  after_create :email_article_author

  def article_should_be_published
    errors.add(:article_id, 'is not published yet') if article && !article.published?
  end

  def email_article_author
    NotifierMailer.comment_added(self).deliver_later
  end
end