Live Queries

Subscribing to Queries to Get Real-Time Alerts Whenever Data in the Query Result Set Changes.

Standard Connection

We maintain a WebSocket connection to communicate with the Moralis LiveQuery server. When used server-side, we use the ws package and in the browser we use window.WebSocket. We think that in most cases it isn't necessary to deal with the WebSocket connection directly. Thus, we developed a simple API to let you focus on your own business logic.

Create a Subscription

Follow this tutorial for a step by step procedure: Tutorial

let query = new Moralis.Query('Game');
let subscription = await query.subscribe();

The subscription you get is actually an event emitter. For more information on event emitter, check here. You'll get the LiveQuery events through this subscription. The first time you call subscribe, we'll try to open the WebSocket connection to the LiveQuery server for you.

Event Handling

We define several types of events you'll get through a subscription object:

Open Event

subscription.on('open', () => {
 console.log('subscription opened');
});

When you call query.subscribe(), we send a subscribe request to the LiveQuery server. When we get the confirmation from the LiveQuery server, this event will be emitted.

When the client fails to maintain the WebSocket connection and gets disconnected to the LiveQuery server, we'll try to auto-reconnect the LiveQuery server. If we reconnect the LiveQuery server and successfully resubscribe the MoralisQuery, you'll also get this event.

Create Event

subscription.on('create', (object) => {
  console.log('object created');
});

When a new MoralisObject is created and it fulfills the MoralisQuery you subscribe, you'll get this event. The object is the MoralisObject which was created.

Note: on a new Nitro server, for tables that are automatically synced, for example for syncing events, update will work instead of create.

Update Event

subscription.on('update', (object) => {
  console.log('object updated');
});

When an existing MoralisObject fulfills the MoralisQuery, your subscribe is updated (The MoralisObject fulfills the MoralisQuery before and after changes), and you'll get this event. The object is the MoralisObject which was updated. Its content is the latest value of the MoralisObject.

Enter Event

subscription.on('enter', (object) => {
  console.log('object entered');
});

When an existing MoralisObject's old value does not fulfill the MoralisQuery but its new value fulfills the MoralisQuery, you'll get this event. The object is the MoralisObject which enters the MoralisQuery. Its content is the latest value of the MoralisObject.

Leave Event

subscription.on('leave', (object) => {
  console.log('object left');
});

When an existing MoralisObject's old value fulfills the MoralisQuery but its new value doesn't fulfill the MoralisQuery, you'll get this event. The object is the MoralisObject which leaves the MoralisQuery. Its content is the latest value of the MoralisObject.

Delete Event

subscription.on('delete', (object) => {
  console.log('object deleted');
});

When an existing MoralisObject which fulfills the MoralisQuery is deleted, you'll get this event. The object is the MoralisObject which is deleted.

Close Event

subscription.on('close', () => {
  console.log('subscription closed');
});

When the client loses its WebSocket connection to the LiveQuery server and we can't get any more events, you'll get this event.

Unsubscribe

subscription.unsubscribe();

If you would like to stop receiving events from a MoralisQuery, you can just unsubscribe the subscription. After that, you won't get any events from the subscription object.

Close

Moralis.LiveQuery.close();

When you are done using LiveQuery, you can call Moralis.LiveQuery.close(). This function will close the WebSocket connection to the LiveQuery server, cancel the auto-reconnect, and unsubscribe all subscriptions based on it. If you call query.subscribe() after this, we will create a new WebSocket connection to the LiveQuery server.

Setup Server URL

Moralis.liveQueryServerURL = 'ws://XXXX'

Most of the time you do not need to manually set this. If you have set up your Moralis.serverURL, we will try to extract the hostname and use ws://hostname as the default liveQueryServerURL. However, if you want to define your own liveQueryServerURL or use a different protocol such as wss, you should set it yourself.

WebSocket Status

We expose three events to help you monitor the status of the WebSocket connection:

Open Event

Moralis.LiveQuery.on('open', () => {
  console.log('socket connection established');
});

When we establish the WebSocket connection to the LiveQuery server, you'll get this event.

Close Event

Moralis.LiveQuery.on('close', () => {
  console.log('socket connection closed');
});

When we lose the WebSocket connection to the LiveQuery server, you'll get this event.

Error Event

Moralis.LiveQuery.on('error', (error) => {
  console.log(error);
});

When a network error or LiveQuery server error happens, you'll get this event.

Reconnect

Since the whole LiveQuery feature relies on the WebSocket connection to the LiveQuery server, we always try to maintain an open WebSocket connection.

Thus, when the connection is lost to the LiveQuery server, we try to auto-reconnect. We do exponential back off under the hood.

However, if the WebSocket connection is closed due to Moralis.LiveQuery.close() or client.close(), we'll cancel the auto-reconnect.

SessionToken

We send sessionToken to the LiveQuery server when you subscribe to a MoralisQuery. For the standard API, we use the sessionToken of the current user by default. For the advanced API, you can use any sessionToken when you subscribe to a MoralisQuery. An important thing to be aware of is when you log out or the sessionToken you are using is invalid, you should unsubscribe from the subscription and subscribe to the MoralisQuery again. Otherwise, you may face a security issue since you'll get events that shouldn't be sent to you.

Example with using Moralis.Query.or with two queries

let query1 = new Moralis.Query('test_subscription');
let query2 = new Moralis.Query('test_subscription');
query1.equalTo('a', undefined)
query2.equalTo('a', '10')
mainQuery = Moralis.Query.or(query1, query2);
let subscription = await mainQuery.subscribe();
subscription.on('create', (object) => {
  console.log('object created', object);
});
subscription.on('update', (object) => {
  console.log('object updated', object);
});

Tutorial