Subscribe to real-time events

In this guide, we will outline the benefits of enabling real-time data integrations and how to set up and filter these subscriptions. We will also cover how to unsubscribe from subscriptions.

Before you begin, you will need:

• An application connected to the API
• Data already created to modify

Set up a real-time list query

The recommended way to fetch a list of data is to use observeQuery to get a real-time list of your app data at all times. You can integrate observeQuery with React's useState and useEffect hooks in the following way:

import { useState, useEffect } from 'react';
import { generateClient } from 'aws-amplify/data';
import type { Schema } from '../amplify/data/resource';

type Todo = Schema['Todo']['type'];

const client = generateClient<Schema>();

export default function MyComponent() {
  const [todos, setTodos] = useState<Todo[]>([]);

  useEffect(() => {
    const sub = client.models.Todo.observeQuery().subscribe({
      next: ({ items, isSynced }) => {
        setTodos([...items]);
      },
    });
    return () => sub.unsubscribe();
  }, []);

  return (
    <ul>
      {todos.map((todo) => (
        <li key={todo.id}>{todo.content}</li>
      ))}
    </ul>
  );
}

observeQuery fetches and paginates through all of your available data in the cloud. While data is syncing from the cloud, snapshots will contain all of the items synced so far and an isSynced status of false. When the sync process is complete, a snapshot will be emitted with all the records in the local store and an isSynced status of true.

Set up a real-time event subscription

Subscriptions is a feature that allows the server to send data to its clients when a specific event happens. For example, you can subscribe to an event when a new record is created, updated, or deleted through the API. Subscriptions are automatically available for any a.model() in your Amplify Data schema.

import { generateClient } from 'aws-amplify/data';
import type { Schema } from '../amplify/data/resource';

const client = generateClient<Schema>();

// Subscribe to creation of Todo
const createSub = client.models.Todo.onCreate().subscribe({
  next: (data) => console.log(data),
  error: (error) => console.warn(error),
});

// Subscribe to update of Todo
const updateSub = client.models.Todo.onUpdate().subscribe({
  next: (data) => console.log(data),
  error: (error) => console.warn(error),
});

// Subscribe to deletion of Todo
const deleteSub = client.models.Todo.onDelete().subscribe({
  next: (data) => console.log(data),
  error: (error) => console.warn(error),
});

// Stop receiving data updates from the subscription
createSub.unsubscribe();
updateSub.unsubscribe();
deleteSub.unsubscribe();

Set up server-side subscription filters

Subscriptions take an optional filter argument to define service-side subscription filters:

import { generateClient } from 'aws-amplify/data';
import type { Schema } from '../amplify/data/resource';

const client = generateClient<Schema>();

const sub = client.models.Todo.onCreate({
  filter: {
    content: {
      contains: 'groceries',
    },
  },
}).subscribe({
  next: (data) => console.log(data),
  error: (error) => console.warn(error),
});

If you want to get all subscription events, don't specify any filter parameters.

Subscription connection status updates

Now that your application is set up and using subscriptions, you may want to know when the subscription is finally established, or reflect to your users when the subscription isn't healthy. You can monitor the connection state for changes through the Hub local eventing system.

import { CONNECTION_STATE_CHANGE, ConnectionState } from 'aws-amplify/data';
import { Hub } from 'aws-amplify/utils';

Hub.listen('api', (data: any) => {
  const { payload } = data;
  if (payload.event === CONNECTION_STATE_CHANGE) {
    const connectionState = payload.data.connectionState as ConnectionState;
    console.log(connectionState);
  }
});

Subscription connection states

• Connected - Connected and working with no issues.
• ConnectedPendingDisconnect - The connection has no active subscriptions and is disconnecting.
• ConnectedPendingKeepAlive - The connection is open, but has missed expected keep-alive messages.
• ConnectedPendingNetwork - The connection is open, but the network connection has been disrupted. When the network recovers, the connection will continue serving traffic.
• Connecting - Attempting to connect.
• ConnectionDisrupted - The connection is disrupted and the network is available.
• ConnectionDisruptedPendingNetwork - The connection is disrupted and the network connection is unavailable.
• Disconnected - Connection has no active subscriptions and is disconnecting.

import { generateClient, CONNECTION_STATE_CHANGE, ConnectionState } from 'aws-amplify/data'
import { Hub } from 'aws-amplify/utils'
import { Schema } from '../amplify/data/resource';

const client = generateClient<Schema>()

const fetchRecentData = () => {
  const { data: allTodos } = await client.models.Todo.list();
}

let priorConnectionState: ConnectionState;

Hub.listen("api", (data: any) => {
  const { payload } = data;
  if (
    payload.event === CONNECTION_STATE_CHANGE
  ) {

    if (priorConnectionState === ConnectionState.Connecting && payload.data.connectionState === ConnectionState.Connected) {
      fetchRecentData();
    }
    priorConnectionState = payload.data.connectionState;
  }
});

const createSub = client.models.Todo.onCreate().subscribe({
  next: payload => // Process incoming messages
});

const updateSub = client.models.Todo.onUpdate().subscribe({
  next: payload => // Process incoming messages
});

const deleteSub = client.models.Todo.onDelete().subscribe({
  next: payload => // Process incoming messages
});

const cleanupSubscriptions = () => {
  createSub.unsubscribe();
  updateSub.unsubscribe();
  deleteSub.unsubscribe();
}

Unsubscribe from a subscription

You can also unsubscribe from events by using subscriptions by implementing the following:

// Stop receiving data updates from the subscription
sub.unsubscribe();

Conclusion

Congratulations! You have finished the Subscribe to real-time events guide. In this guide, you set up subscriptions for real-time events and learned how to filter and cancel these subscriptions when needed.

Next steps

Our recommended next steps include continuing to build out and customize your information architecture for your data. Some resources that will help with this work include:

• Customize your auth rules
• Customize your data model
• Add custom business logic