Need index to allow efficiently deleting notifications

[tspacek]

def destroy_singular_notifications(klass)
  klass.select('notify_user_notifications.*')
    .from("notify_user_notifications, to_json(notify_user_notifications.params -> 'user') user_entry")
    .where("user_entry ->> 'id' = ?", user.id).destroy_all
end

Need to be able to efficiently query on the subject of a notification, not just the target to whom the notification is sent. So that we can delete notifications for content that has been deleted or no longer warrants a notification.

[knightstick]

We also need to be able to destroy all notifications related to a particular object:

notification_classes.each do |klass|
  klass.public_send(:where, 'params ->> \'group_id\' = ?', vent.id).destroy_all
end