Perché Firestore richiede un indice composito per alcune query?

Firestore richiede un indice composito quando una query combina più condizioni where() su campi diversi, oppure where() e orderBy() su campi diversi: senza un indice dedicato, Firestore non potrebbe eseguire la query in modo efficiente.

Come si crea rapidamente l'indice richiesto?

Quando la query fallisce per mancanza di indice, Firestore restituisce un errore con un link diretto alla console che pre-compila i campi necessari: basta seguirlo e confermare la creazione.

Creare molti indici compositi ha un costo?

Sì, ogni indice composito viene aggiornato a ogni scrittura sui campi coinvolti, aumentando leggermente il costo e il tempo delle operazioni di scrittura: è quindi utile creare solo gli indici effettivamente necessari.

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Firestore Firebase Indice composito JavaScript SDK v9

Firestore: compound query with multiple filters and composite index

When you filter a Firestore collection with multiple where() conditions combined with orderBy(), Firestore requires a composite index. The console error already includes a link to create it — but you need to know what's happening.

Compound query — SDK v9

firestore-query.js

import {
  getFirestore, collection, query,
  where, orderBy, limit, getDocs
} from 'firebase/firestore';

const db = getFirestore();

/**
 * Recupera le richieste di un operatore degli ultimi N giorni.
 * Questa query richiede un indice composito su:
 *   [operatorId ASC, tipo ASC, timestamp DESC]
 */
async function getRecentRequests(operatorId, giorni = 90) {
  const cutoff = Date.now() - giorni * 24 * 60 * 60 * 1000;

  const q = query(
    collection(db, 'activityLog'),
    where('operatorId', '==', operatorId),
    where('tipo',       'in', ['ferie', 'permesso', 'malattia']),
    where('timestamp',  '>=', cutoff),
    orderBy('timestamp', 'desc'),
    limit(100)
  );

  const snap = await getDocs(q);
  return snap.docs.map(d => ({ id: d.id, ...d.data() }));
}

Typical console error:
FirebaseError: The query requires an index. You can create it here: https://console.firebase.google.com/...

The link in the error goes directly to the index creation page. Click it and wait 1-2 minutes.

How a composite index works

Firestore automatically creates indexes for every individual field. When you combine multiple fields in a query — especially using orderBy() on a different field from the one being filtered — Firestore can't use single-field indexes and requires a composite one covering all fields involved.

Practical rules:

Simple equality == on one field → no composite index needed
Two or more where() on different fields → composite index required
where() + orderBy() on different fields → composite index required
in, array-contains-any → require an index when combined with other filters

Create the index manually (without waiting for the error)

firestore.indexes.json — deploy con Firebase CLI

{
  "indexes": [
    {
      "collectionGroup": "activityLog",
      "queryScope": "COLLECTION",
      "fields": [
        { "fieldPath": "operatorId", "order": "ASCENDING"  },
        { "fieldPath": "tipo",       "order": "ASCENDING"  },
        { "fieldPath": "timestamp", "order": "DESCENDING" }
      ]
    }
  ],
  "fieldOverrides": []
}

Recommended strategy: develop locally, let the console error give you the link the first time, click to create the index, then export the config with firebase firestore:indexes and commit it to your project.

Limits to keep in mind

Firestore supports a maximum of 200 composite indexes per project
A query with in on N values runs N sub-queries internally
You can't have two inequality filters (>, <) on different fields in the same query
The index takes 1-3 minutes to become active — reload the page after creation

PWA notification centre: six categories, two databases — Firestore in production

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Custom Firebase e-commerce: Firestore queries for variants, atomic orders and admin panel

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Firestore: compound query with multiple filters and composite index

Compound query — SDK v9

How a composite index works

Create the index manually (without waiting for the error)

Limits to keep in mind

When you need a composite index in Firestore

When to use it

When NOT to use it

Alternatives

Common mistakes

Frequently asked questions about Firestore composite indexes