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

Monitor Database Changes with MongoDB Change Streams

📖 Scenario: You are managing a MongoDB database for an online bookstore. You want to track any changes made to the books collection in real-time to update your inventory system promptly.

🎯 Goal: Build a MongoDB change stream that listens to changes on the books collection and captures insert, update, and delete events.

📋 What You'll Learn

Create a MongoDB collection named books with sample documents.

Define a change stream on the books collection.

Configure the change stream to listen for insert, update, and delete operations.

Implement the change stream to print the change events.

💡 Why This Matters

🌍 Real World

Change streams help applications react instantly to database changes, such as updating user interfaces or syncing data across services.

💼 Career

Understanding change streams is valuable for backend developers and database administrators who build real-time data-driven applications.

1

Create the books collection with sample data

Create a MongoDB collection called books and insert these exact documents: { _id: 1, title: "The Hobbit", author: "J.R.R. Tolkien" } and { _id: 2, title: "1984", author: "George Orwell" }.

MongoDB

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

Need a hint?

Use db.books.insertMany() with an array of documents.

2

Define a change stream cursor on the books collection

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

MongoDB

db.books.insertMany([
  { _id: 1, title: "The Hobbit", author: "J.R.R. Tolkien" },
  { _id: 2, title: "1984", author: "George Orwell" }
])

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

Need a hint?

Use db.books.watch() to create the change stream cursor.

3

Configure the change stream to filter for insert, update, and delete events

Modify the changeStream to watch only for insert, update, and delete operation types by passing a pipeline with $match to db.books.watch().

MongoDB

db.books.insertMany([
  { _id: 1, title: "The Hobbit", author: "J.R.R. Tolkien" },
  { _id: 2, title: "1984", author: "George Orwell" }
])

// Update changeStream to filter for insert, update, and delete events
// Your code here

Need a hint?

Pass a pipeline array with { $match: { operationType: { $in: [...] } } } to db.books.watch().

4

Listen for change events and print them

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

MongoDB

db.books.insertMany([
  { _id: 1, title: "The Hobbit", author: "J.R.R. Tolkien" },
  { _id: 2, title: "1984", author: "George Orwell" }
])

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

// Add an event listener on changeStream to log change events
// Your code here

Need a hint?

Use changeStream.on('change', (change) => { console.log(change) }) to listen and print events.