onDBDelete.js

import("system.vars");
import("system.notification");

// Deletes notificationContents from its table, if there are no user notification left
// Only AppointmentContents need to stay, because they would appear again after every deletion.
if(vars.get("$field.TYPECODE") != "_____SYSTEM_NOTIFICATION_APPOINTMENT")
    notification.deleteMultipleContentsIfOrphan([vars.get("$field.CONTENTID")]);