Multi-category notification center: Firestore + RTDB in the same drawer

The problem

A notification center with multiple categories (leave requests, calendar, chat, reminders) often has data living in different databases with different characteristics: some need a one-time read, others need real-time updates. Using the same pattern for everything wastes reads or introduces unnecessary listeners.

Firestore: single read with multiple filters

For categories where history doesn't change often (e.g. leave requests), a Firestore query with .get() — not .onSnapshot() — avoids keeping an unnecessary listener open.

const cutoff = Date.now() - 90 * 24 * 60 * 60 * 1000;
const tipi = [
  'ferie_richiesta', 'ferie_approvata',
  'ferie_rifiutata', 'ferie_annullata'
];

db.collection('activityLog')
  .where('operatore', '==', currentUser)
  .where('tipo', 'in', tipi)
  .where('ts', '>=', cutoff)
  .get()   // una sola lettura, non real-time
  .then(snap => snap.docs.map(d => ({ id: d.id, ...d.data() })));

RTDB: real-time listeners on existing nodes

Calendar, reminders and chat instead live on the Realtime Database — small nodes, already structured for fast reads. Attaching with .on('value') to existing nodes doesn't add significant cost, and it's the right choice when data changes often and the user needs to see updates without refreshing.

const ref = db.ref('calendario/' + reparto);

ref.on('value', snapshot => {
  const eventi = snapshot.val() || {};

  // Filtra: solo eventi già scattati, creati dall'utente o del suo reparto
  const visibili = Object.entries(eventi)
    .filter(([id, ev]) =>
      ev.firedAt && (ev.creatoDa === currentUser || ev.reparto === userReparto)
    );

  renderNotificheCalendario(visibili);
});

// Da chiamare allo smontaggio del componente / cambio utente
function cleanup() { ref.off('value'); }