Suscripciones en tiempo real
Suscríbase a los cambios de la base de datos con supabase.channel, escuche eventos INSERT y UPDATE en una tabla y actualice de forma reactiva el estado local de la interfaz sin realizar polling.
Suscripciones en tiempo real es una lección gratuita de React Native Academy en CoddyKit. Esta es la lección 4 de 4. Puedes leer la lección completa abajo gratuitamente — luego la practicas en el navegador con un editor de código integrado y un tutor de IA 24/7. Forma parte de la ruta de aprendizaje de React Native Academy, y tu progreso se sincroniza en la web y la app de CoddyKit. El curso de React Native Academy incluye 4 lecciones en total.
Partes de esta lección aún no han sido traducidas y se muestran en inglés.
What Are Real-Time Subscriptions?
Real-time subscriptions allow your React Native app to receive database changes as they happen, without polling. When another user inserts, updates, or deletes a row, Supabase pushes the change to all subscribed clients over a WebSocket connection.
This is ideal for chat apps, live feeds, collaborative tools, and any feature where multiple users interact with shared data. Supabase's real-time engine is built on PostgreSQL's logical replication and the supabase-js client handles the WebSocket lifecycle for you.
Enabling Real-Time on a Table
Before subscribing to changes, you must enable real-time replication for the table in Supabase. Go to the Supabase dashboard, open Database > Replication, and add the table to the supabase_realtime publication.
You can also do this with SQL: ALTER PUBLICATION supabase_realtime ADD TABLE your_table;. Without this step, your subscription will connect but receive no events, which is a common source of confusion when first setting up real-time.
-- Enable real-time for the 'messages' table
ALTER PUBLICATION supabase_realtime ADD TABLE messages;
-- Verify which tables have real-time enabled:
SELECT tablename FROM pg_publication_tables
WHERE pubname = 'supabase_realtime';Creating a Channel and Subscribing
Subscriptions in Supabase v2 are created with supabase.channel('channel-name'). You attach one or more event listeners with .on('postgres_changes', filter, callback), then call .subscribe() to start the WebSocket connection.
The filter object specifies the event (INSERT, UPDATE, DELETE, or * for all), the schema, and the table. The callback receives a payload object with the changed data.
const channel = supabase
.channel('messages-changes')
.on(
'postgres_changes',
{ event: '*', schema: 'public', table: 'messages' },
(payload) => {
console.log('Change received:', payload);
}
)
.subscribe();
// Unsubscribe when done:
// supabase.removeChannel(channel);The Payload Structure
The payload object passed to your callback contains the change details:
- eventType — 'INSERT', 'UPDATE', or 'DELETE'
- new — the new row data (available for INSERT and UPDATE)
- old — the previous row data (available for UPDATE and DELETE)
- schema and table — which table changed
For DELETE events, payload.new is an empty object and payload.old contains the deleted row. For INSERT, payload.old is empty.
supabase
.channel('messages-changes')
.on(
'postgres_changes',
{ event: 'INSERT', schema: 'public', table: 'messages' },
(payload) => {
// payload.eventType === 'INSERT'
// payload.new === { id: '...', text: 'Hello!', user_id: '...' }
// payload.old === {}
console.log('New message:', payload.new);
}
)
.subscribe();Updating State on Real-Time Events
The most common pattern is to update a state array when a real-time event arrives. For INSERT events, append the new row. For UPDATE, replace the matching row. For DELETE, filter the row out.
Be careful to use the functional form of the state setter (setMessages(prev => [...])) to always work with the latest state, since the subscription callback is a closure that captures the state at subscription time.
const [messages, setMessages] = useState([]);
useEffect(() => {
const channel = supabase
.channel('messages-live')
.on('postgres_changes',
{ event: 'INSERT', schema: 'public', table: 'messages' },
(payload) => {
setMessages(prev => [payload.new, ...prev]);
}
)
.on('postgres_changes',
{ event: 'DELETE', schema: 'public', table: 'messages' },
(payload) => {
setMessages(prev => prev.filter(m => m.id !== payload.old.id));
}
)
.subscribe();
return () => { supabase.removeChannel(channel); };
}, []);Filtering Subscriptions by Column Value
To subscribe only to changes in rows relevant to the current user or room, add a filter string to the event options. The filter syntax is 'column_name=eq.value', similar to PostgREST query syntax.
This reduces unnecessary network traffic on the client and avoids processing changes that are not relevant to the current screen. For example, in a chat app, subscribe only to messages in the current room.
const roomId = 'room-42';
const channel = supabase
.channel('room-messages')
.on(
'postgres_changes',
{
event: '*',
schema: 'public',
table: 'messages',
filter: 'room_id=eq.' + roomId,
},
(payload) => {
// Only fires for messages in room-42
console.log('Room message event:', payload);
}
)
.subscribe();Broadcast: Real-Time Without a Database
Supabase channels also support Broadcast, which lets you send ephemeral messages to all clients subscribed to the same channel without writing to the database. This is perfect for typing indicators, cursor positions, or transient presence events.
Use .on('broadcast', { event: 'typing' }, callback) to receive broadcast messages and channel.send to send them. Broadcast messages are not stored and do not trigger RLS policies.
const channel = supabase.channel('typing-indicators');
// Listen for typing events
channel.on('broadcast', { event: 'typing' }, (payload) => {
console.log(payload.payload.username, 'is typing...');
}).subscribe();
// Send a typing event
async function sendTypingIndicator(username: string) {
await channel.send({
type: 'broadcast',
event: 'typing',
payload: { username },
});
}Presence: Tracking Online Users
Presence is a Supabase feature that lets you track which users are currently online and share state between them. Each client tracks its own presence, and the channel aggregates the presence of all connected clients in real time.
This is ideal for showing an online indicator next to user avatars in a chat list or a participants sidebar in a collaborative document.
const channel = supabase.channel('online-users');
channel
.on('presence', { event: 'sync' }, () => {
const state = channel.presenceState();
console.log('Currently online:', Object.keys(state));
})
.subscribe(async (status) => {
if (status === 'SUBSCRIBED') {
await channel.track({ user_id: currentUserId, online_at: new Date().toISOString() });
}
});
// Untrack when leaving the screen
// await channel.untrack();Cleaning Up Subscriptions in useEffect
Real-time channels use WebSocket connections. It is critical to clean up by calling supabase.removeChannel(channel) when the component unmounts. If you forget to clean up, you will accumulate WebSocket connections and leak memory.
Return a cleanup function from useEffect that removes the channel. React calls this cleanup automatically when the component unmounts or before the effect re-runs due to dependency changes.
useEffect(() => {
const channel = supabase
.channel('my-channel')
.on('postgres_changes',
{ event: '*', schema: 'public', table: 'messages' },
handleChange
)
.subscribe();
// Cleanup: remove channel on unmount
return () => {
supabase.removeChannel(channel);
};
}, []); // Run once on mount, clean up on unmountBuilding a Real-Time Chat Screen
A real-time chat screen combines an initial useEffect fetch for existing messages with a real-time subscription for new ones. Fetch the last 50 messages on mount, then append new messages as they arrive via INSERT events.
Use an inverted FlatList (inverted prop) so the newest message always appears at the bottom without needing to scroll. Render each message as a row with the sender's avatar and text.
export function ChatScreen({ roomId }: { roomId: string }) {
const [messages, setMessages] = useState([]);
useEffect(() => {
// 1. Fetch existing messages
supabase
.from('messages')
.select('*, sender:profiles(username)')
.eq('room_id', roomId)
.order('created_at', { ascending: false })
.limit(50)
.then(({ data }) => setMessages(data ?? []));
// 2. Subscribe to new messages
const channel = supabase
.channel('room-' + roomId)
.on('postgres_changes',
{ event: 'INSERT', schema: 'public', table: 'messages',
filter: 'room_id=eq.' + roomId },
(payload) => setMessages(prev => [payload.new, ...prev])
)
.subscribe();
return () => { supabase.removeChannel(channel); };
}, [roomId]);
return <FlatList inverted data={messages} renderItem={({ item }) =>
<MessageRow message={item} />
} />;
}Subscription Status and Error Handling
The .subscribe() method accepts an optional callback that receives the subscription status. You can use this to show connection indicators in your UI or retry logic when the subscription fails.
Possible status values include 'SUBSCRIBED' (active), 'TIMED_OUT', 'CLOSED', and 'CHANNEL_ERROR'. Always handle error states to give users feedback when real-time functionality is unavailable.
const channel = supabase
.channel('live-feed')
.on('postgres_changes',
{ event: '*', schema: 'public', table: 'posts' },
handleChange
)
.subscribe((status) => {
if (status === 'SUBSCRIBED') {
setConnectionStatus('Live');
} else if (status === 'CHANNEL_ERROR') {
setConnectionStatus('Disconnected');
} else if (status === 'TIMED_OUT') {
setConnectionStatus('Reconnecting...');
}
});Quick Check
Test your understanding of React Native Mobile Development concepts from this lesson.
Lesson Recap
In this lesson you learned: how to subscribe to Postgres changes with supabase.channel, how to filter subscriptions by column value for targeted updates, and how to properly clean up channels on component unmount to avoid WebSocket leaks. Next up we explore integrating Firebase Auth and Firestore as an alternative backend for React Native apps.
Preguntas frecuentes
¿La lección «Suscripciones en tiempo real» es gratis?
Sí — el texto completo de «Suscripciones en tiempo real» es gratis para leer aquí en la web. Para practicarla de forma interactiva (editor de código integrado y tutor de IA 24/7) y desbloquear el resto del curso de React Native Academy, actualiza a CoddyKit PRO. El curso de React Native Academy incluye 4 lecciones en total.
¿Qué aprenderé en «Suscripciones en tiempo real»?
Suscríbase a los cambios de la base de datos con supabase.channel, escuche eventos INSERT y UPDATE en una tabla y actualice de forma reactiva el estado local de la interfaz sin realizar polling. Practicas React Native Academy con código real que ejecutas directamente en el navegador, y un tutor de IA 24/7 responde tus preguntas mientras trabajas en la lección.
¿Necesito experiencia previa para empezar React Native Academy?
No se requiere experiencia previa. React Native Academy en CoddyKit está estructurado para principiantes hasta estudiantes avanzados, así que puedes empezar aquí o desde el inicio y avanzar a tu ritmo. Esta es la lección 4 de 4.
¿Cuánto tiempo toma la lección «Suscripciones en tiempo real»?
La mayoría de las lecciones de CoddyKit toman alrededor de 5–10 minutos. Cada una es compacta e interactiva, así que avanzas constantemente y retomas exactamente por donde dejaste en la web y la app.
¿Puedo escribir y ejecutar código en esta lección de React Native Academy?
Sí. Cada lección de React Native Academy incluye un editor de código integrado, así que escribes y ejecutas código real directamente en tu navegador y obtienes retroalimentación instantánea de IA — sin configuración local necesaria.
Todas las lecciones de este curso
- Configuración del cliente de Supabase en React Native
- Autenticación por correo electrónico y OAuth
- Consulta de la base de datos con el cliente de Supabase
- Suscripciones en tiempo real