Use cases for change streams in MongoDB

Introduction

Change streams let you watch for changes in your database in real time. This helps you react quickly when data updates happen.

You want to update a live dashboard when new data arrives.

You need to sync data changes from one database to another automatically.

You want to send notifications when important data changes.

You want to audit or log all changes happening in your database.

You want to trigger other processes when data is inserted, updated, or deleted.

Syntax

MongoDB

const changeStream = collection.watch(pipeline, options);

The 'pipeline' lets you filter which changes to watch.

The 'options' can control things like full document retrieval.

Examples

Watch all changes on the collection without filters.

MongoDB

const changeStream = collection.watch();

Watch only insert operations.

MongoDB

const changeStream = collection.watch([{ $match: { operationType: 'insert' }}]);

Get the full updated document on update events.

MongoDB

const changeStream = collection.watch([], { fullDocument: 'updateLookup' });

Sample Program

This program watches the 'orders' collection for new inserts. When a new order is added, it prints the order details.

MongoDB

const { MongoClient } = require('mongodb');

async function watchInserts() {
  const client = new MongoClient('mongodb://localhost:27017');
  await client.connect();
  const db = client.db('shop');
  const collection = db.collection('orders');

  const changeStream = collection.watch([{ $match: { operationType: 'insert' } }]);

  console.log('Watching for new orders...');
  changeStream.on('change', (change) => {
    console.log('New order inserted:', change.fullDocument);
  });
}

watchInserts();

Important Notes

Change streams require a replica set or sharded cluster in MongoDB.

They provide real-time notifications without polling the database.

You can filter changes to reduce noise and focus on relevant events.

Summary

Change streams help you react instantly to database changes.

Use them for live updates, syncing, notifications, and auditing.

You can filter and customize what changes to watch.