Firebase Firestore: Real-Time App Databases

What Is Cloud Firestore?

A serverless, real-time document database from Google: how it differs from SQL and MongoDB, and when to choose it.

Setup: Firebase Project, Console & Emulator

Create a Firebase project, add a web app, initialise Firestore in the SDK, and run the local Emulator Suite.

Collections, Documents & Subcollections

How Firestore organises data: paths, document ids, field types and subcollections.

Writing Data: add, set, update & delete

Create documents with auto or custom ids, merge updates, increment counters, and use server timestamps.

Reading Data: getDoc & getDocs

Read a single document or a whole collection, handle missing documents, and convert timestamps.

Queries, Ordering & Indexes

Filter with where, sort with orderBy, limit results, combine conditions, and create composite indexes.

Pagination with Cursors

Load lists page by page with startAfter cursors, for infinite scroll that stays fast and cheap.

Real-Time Listeners

Subscribe to documents and queries with onSnapshot, react to added/modified/removed changes, and unsubscribe properly.

Offline Support

Let apps keep working without a connection: local cache, pending writes and the hasPendingWrites flag.

Modelling Data for Firestore

Design for your screens: denormalise, store counters, use subcollections, and avoid hot spots.

Firebase Authentication

Add email, Google and phone sign-in, react to auth state, and link users to their Firestore profile.

Security Rules: Who Can Read and Write

Write Firestore security rules that check authentication, ownership and roles, the real backend of a Firebase app.

Validating Data in Rules

Use rules to enforce required fields, types, sizes and allowed values, and to stop users changing protected fields.

Testing Rules with the Emulator

Prove your security rules work with automated tests using the Emulator Suite and @firebase/rules-unit-testing.

Cloud Storage for Photos & Files

Upload photos with Firebase Storage, save the download URL in Firestore, and protect files with storage rules.

Transactions & Batched Writes

Make multiple writes atomic with batches, and read-then-write safely with transactions.

Cloud Functions: Server Code When You Need It

Run trusted server code on Firestore triggers, HTTP requests and schedules: counters, notifications and payment webhooks.

Building a Web App with Firestore

Structure a Firestore web app: a data layer, reusable listeners, loading and error states, and hosting.

Costs, Limits & Performance

Understand Firestore billing, stay inside the free tier, avoid expensive patterns and set budget alerts.

Project: A Chama Contributions App

Build a real-time, offline-ready app for savings groups with Firestore, Auth, rules, Cloud Functions and Hosting.