tab/app/controllers/notifications_controller.rb

class NotificationsController < ApplicationController
  load_and_authorize_resource :user, only: :index

  before_action :load_notification, only: :read
  authorize_resource :notification, only: :read

  def index
    @notifications = @user.notifications.group_by(&:read)
  end

  def read
    @notification.read!
    redirect_to root_path
  end

  private

  def load_notification
    @notification = Notification.find params[:notification_id]
  end
end