# For most notification types, only one notification should exist, and the older one is
    # preferred. For updates, such as when a status is edited, the new notification
    # should replace the previous ones.
    if type == 'update'
      Notification.where(account: receiver, activity: activity, type: 'update').in_batches.delete_all
    elsif Notification.where(account: receiver, activity: activity, type: type).any?
      return
    end