def open_receiver_class
      # Define association for receiver model
      [receivers_class(@@options[:receivers])].flatten.each do |base|
        base.class_eval do
          has_many :deliveries, class_name: 'SimpleNotifications::Delivery', as: :receiver
          has_many :received_notifications, through: :deliveries, source: :simple_notification
        end
      end
    end
def open_receiver_class
      # Define association for receiver model
      [receivers_class(@@options[:receivers])].flatten.each do |base|
        base.class_eval do
          has_many :deliveries, class_name: 'SimpleNotifications::Delivery', as: :receiver
          has_many :received_notifications, through: :deliveries, source: :simple_notification
        end
      end
    end
Opening the classes which are defined as receivers.