Use cases for change streams in MongoDB - Mini Project: Build & Apply

Use Cases for Change Streams in MongoDB

📖 Scenario: You are building a real-time notification system for an online store. You want to track changes in the orders collection to notify the sales team immediately when a new order is placed or an existing order is updated.

🎯 Goal: Create a MongoDB change stream to watch the orders collection for insert and update events, and prepare the system to handle these changes.

📋 What You'll Learn

Create a MongoDB collection named orders with sample documents.

Define a change stream on the orders collection.

Filter the change stream to listen only for insert and update operations.

Set up a basic handler to process the change events.

💡 Why This Matters

🌍 Real World

Change streams allow applications to react immediately to database changes, enabling real-time features like notifications, analytics, and synchronization.

💼 Career

Understanding change streams is valuable for backend developers, database administrators, and anyone building reactive or event-driven applications with MongoDB.

1

Create the orders collection with sample data

Create a MongoDB collection called orders and insert these exact documents: { _id: 1, item: "laptop", quantity: 2 } and { _id: 2, item: "phone", quantity: 5 }.

MongoDB

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

Need a hint?

Use insertMany on db.orders with an array of the two documents.

2

Define a change stream on the orders collection

Create a variable called changeStream that watches the orders collection using db.orders.watch().

MongoDB

db.orders.insertMany([
  { _id: 1, item: "laptop", quantity: 2 },
  { _id: 2, item: "phone", quantity: 5 }
])

// Create a change stream on the orders collection
// Your code here

Need a hint?

Use db.orders.watch() and assign it to changeStream.

3

Filter the change stream for insert and update events

Modify the changeStream to watch only for insert and update operations by passing a pipeline with $match on operationType equal to insert or update.

MongoDB

db.orders.insertMany([
  { _id: 1, item: "laptop", quantity: 2 },
  { _id: 2, item: "phone", quantity: 5 }
])

// Create a filtered change stream for insert and update
// Your code here

Need a hint?

Pass an array with a $match stage to db.orders.watch() filtering operationType with $in.

4

Set up a handler to process change events

Add a listener to changeStream using changeStream.on('change', callback) where the callback receives a change object and logs the operationType and fullDocument fields.

MongoDB

db.orders.insertMany([
  { _id: 1, item: "laptop", quantity: 2 },
  { _id: 2, item: "phone", quantity: 5 }
])

const changeStream = db.orders.watch([
  { $match: { operationType: { $in: ["insert", "update"] } } }
], { fullDocument: "updateLookup" })

// Add a change event listener to changeStream
// Your code here

Need a hint?

Use changeStream.on('change', callback) and inside the callback access change.operationType and change.fullDocument.