Welcome to the exciting world of realtime updates with Supabase! In this section, we'll demystify the core concepts behind Supabase Realtime, empowering you to build applications that instantly react to changes. Think of it as a persistent, two-way communication channel between your client (your web app, mobile app, etc.) and your Supabase database.
At its heart, Supabase Realtime leverages PostgreSQL's robust change data capture (CDC) capabilities. When data in your Supabase database changes (inserts, updates, deletes), Supabase automatically publishes these events. Your application can then subscribe to these events and react in real-time, without needing to constantly poll the database for new information. This makes your applications feel incredibly responsive and dynamic.
The primary mechanism for this communication is through subscriptions. You can subscribe to specific tables, or even to specific rows within a table, and receive notifications whenever changes occur. Supabase provides a simple and intuitive JavaScript client library to manage these subscriptions.
import { createClient } from '@supabase/supabase-js'
const supabaseUrl = 'YOUR_SUPABASE_URL'
const supabaseKey = 'YOUR_SUPABASE_ANON_KEY'
const supabase = createClient(supabaseUrl, supabaseKey)
// Subscribe to changes in the 'messages' table
const channel = supabase.channel('messages', {
config: {
presence: {
key: 'user_id'
}
}
})
channel.on('postgres_changes', {
event: '*', // Listen to all events (INSERT, UPDATE, DELETE)
schema: 'public',
table: 'messages',
}, (payload) => {
console.log('New message received!', payload)
})
channel.subscribe((status) => {
if (status === 'SUBSCRIBED') {
console.log('Successfully subscribed to messages!')
}
})
// To unsubscribe later:
// channel.unsubscribe()When a change occurs, Supabase Realtime broadcasts an event payload. This payload contains crucial information about the change, including the event type (insert, update, delete), the table affected, the schema, and importantly, the new and/or old record data. This allows your application to precisely understand what changed and how to update its UI accordingly.
graph TD
A[Client Application] --> B(Supabase SDK)
B --> C{Supabase Realtime Server}
C --> D[PostgreSQL CDC]
D -- Detects Changes --> C
C -- Broadcasts Events --> B
B -- Receives Events --> A