Change streams on collections in MongoDB - Mini Project: Build & Apply

Monitor Real-Time Changes with MongoDB Change Streams

📖 Scenario: You are building a simple inventory system for a small store. You want to watch for any changes in the products collection so you can update your dashboard in real-time whenever a product is added, updated, or deleted.

🎯 Goal: Create a MongoDB change stream on the products collection to listen for all changes and print the change events.

📋 What You'll Learn

Create a MongoDB collection named products with some sample documents.

Set up a change stream on the products collection.

Listen for all change events (insert, update, delete).

Print the change event documents as they occur.

💡 Why This Matters

🌍 Real World

Change streams help applications react instantly to database changes, like updating dashboards, syncing data, or triggering alerts.

💼 Career

Understanding change streams is useful for backend developers, database administrators, and anyone building real-time data-driven applications.

1

Create the products collection with sample data

Create a MongoDB collection called products and insert these exact documents: { _id: 1, name: "Apple", quantity: 50 }, { _id: 2, name: "Banana", quantity: 30 }, and { _id: 3, name: "Orange", quantity: 20 }.

MongoDB

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

Need a hint?

Use db.products.insertMany([...]) to add multiple documents at once.

2

Create a change stream cursor on the products collection

Create a variable called changeStream that opens a change stream on the products collection using db.products.watch().

MongoDB

db.products.insertMany([
  { _id: 1, name: "Apple", quantity: 50 },
  { _id: 2, name: "Banana", quantity: 30 },
  { _id: 3, name: "Orange", quantity: 20 }
])

// Create the changeStream variable to watch the products collection
// Your code here

Need a hint?

Use const changeStream = db.products.watch() to start watching changes.

3

Listen for change events using the change stream cursor

Use a while loop with await changeStream.hasNext() and inside the loop assign const change = await changeStream.next() to get each change event.

MongoDB

db.products.insertMany([
  { _id: 1, name: "Apple", quantity: 50 },
  { _id: 2, name: "Banana", quantity: 30 },
  { _id: 3, name: "Orange", quantity: 20 }
])

const changeStream = db.products.watch()

// Use a while loop to wait for new change events
// Your code here

Need a hint?

Use while (await changeStream.hasNext()) to wait for changes and const change = await changeStream.next() to get each event.

4

Print each change event inside the loop

Inside the while loop, add printjson(change) to display the change event document.

MongoDB

db.products.insertMany([
  { _id: 1, name: "Apple", quantity: 50 },
  { _id: 2, name: "Banana", quantity: 30 },
  { _id: 3, name: "Orange", quantity: 20 }
])

const changeStream = db.products.watch()

while (await changeStream.hasNext()) {
  const change = await changeStream.next()
  // Print the change event document
  // Your code here
}

Need a hint?

Use printjson(change) to nicely print the change event document.