Watch method for real-time updates in MongoDB - Mini Project: Build & Apply

Real-Time Updates with MongoDB Watch Method

📖 Scenario: You are building a simple notification system for a small online store. You want to watch the orders collection in MongoDB to get real-time updates whenever a new order is placed.

🎯 Goal: Create a MongoDB watch method setup that listens for new inserts in the orders collection and logs the change events.

📋 What You'll Learn

Create a MongoDB collection named orders with sample order documents.

Set up a watch method on the orders collection to listen for insert events.

Log the change events to the console in real-time.

Use the watch method with a pipeline to filter only insert operations.

💡 Why This Matters

🌍 Real World

Real-time monitoring of database changes is useful for notifications, analytics, and syncing data across systems.

💼 Career

Understanding MongoDB change streams is valuable for backend developers working with real-time applications and event-driven architectures.

1

Create the orders collection with sample data

Create a MongoDB collection called orders and insert these exact documents: { _id: 1, item: 'Book', quantity: 3 } and { _id: 2, item: 'Pen', quantity: 10 }.

MongoDB

// Insert the sample documents into the orders collection
// Your code here

Need a hint?

Use insertMany on db.orders to add multiple documents at once.

2

Define a change stream pipeline to filter insert operations

Create a variable called pipeline that filters change events to only include those where operationType is 'insert'.

MongoDB

db.orders.insertMany([
  { _id: 1, item: 'Book', quantity: 3 },
  { _id: 2, item: 'Pen', quantity: 10 }
])

// Define the pipeline to filter for insert operations
// Your code here

Need a hint?

Use $match in the pipeline to filter for operationType: 'insert'.

3

Start watching the orders collection with the pipeline

Create a variable called changeStream that calls db.orders.watch(pipeline) to start watching for insert events.

MongoDB

db.orders.insertMany([
  { _id: 1, item: 'Book', quantity: 3 },
  { _id: 2, item: 'Pen', quantity: 10 }
])

const pipeline = [
  { $match: { operationType: 'insert' } }
]

// Start watching the orders collection with the pipeline
// Your code here

Need a hint?

Use db.orders.watch(pipeline) to create the change stream.

4

Listen for change events and log them

Use changeStream.on('change', callback) to listen for change events and log the event document using console.log(change) inside the callback function.

MongoDB

db.orders.insertMany([
  { _id: 1, item: 'Book', quantity: 3 },
  { _id: 2, item: 'Pen', quantity: 10 }
])

const pipeline = [
  { $match: { operationType: 'insert' } }
]

const changeStream = db.orders.watch(pipeline)

// Listen for change events and log them
// Your code here

Need a hint?

Use changeStream.on('change', callback) to handle real-time updates.