jumpstart/app/models/notification.rb

class Notification < ApplicationRecord
  belongs_to :recipient, class_name: "User"
  belongs_to :actor, class_name: "User"
  belongs_to :notifiable, polymorphic: true

  def self.post(to:, from:, action:, notifiable:)
    recipients = Array.wrap(to)
    notifications = []

    Notification.transaction do
      notifications = recipients.uniq.each do |recipient|
        Notification.create(
          notifiable: notifiable,
          action:     action,
          recipient:  recipient,
          actor:      from
        )
      end
    end
    notifications
  end
end