Why change streams are needed in MongoDB - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to watch for changes in the 'orders' collection.

MongoDB

const changeStream = db.collection('orders').[1]();

Drag options to blanks, or click blank then click option'

Aupdate

Bfind

Cinsert

Dwatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using find() instead of watch() will only query existing data, not listen for changes.

Using insert() or update() are operations to modify data, not to watch changes.

The watch() method opens a change stream to listen for changes in a collection.

2fill in blank

medium

Complete the code to handle change events from the change stream.

MongoDB

changeStream.on('[1]', next => { console.log(next); });

Drag options to blanks, or click blank then click option'

Achange

Bclose

Cerror

Dopen

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'error' listens for errors, not data changes.

Using 'close' or 'open' are lifecycle events, not change notifications.

The change event fires when a change occurs in the watched collection.

3fill in blank

hard

Fix the error in the code to properly start watching changes on the 'users' collection.

MongoDB

const stream = db.collection('users').[1]();

Drag options to blanks, or click blank then click option'

Alisten

Bwatch

Con

Dsubscribe

Attempts:

3 left

💡 Hint

Common Mistakes

Passing 'change' as argument to watch() causes an error.

Using listen() or subscribe() are not valid MongoDB methods.

The watch() method does not take an event name as argument; it returns a change stream. The event name is used with on().

4fill in blank

hard

Fill both blanks to filter change events for only 'insert' operations.

MongoDB

const pipeline = [ { $match: { 'operationType': [1] } } ];
const stream = db.collection('products').[2](pipeline);

Drag options to blanks, or click blank then click option'

A'insert'

B'update'

Cwatch

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'update' instead of 'insert' filters the wrong operation.

Using find() instead of watch() does not create a change stream.

The pipeline filters for 'insert' operations, and watch() starts the change stream with that filter.

5fill in blank

hard

Fill all three blanks to create a change stream that listens for deletes and logs the document key.

MongoDB

const pipeline = [ { $match: { 'operationType': [1] } } ];
const stream = db.collection('logs').[2](pipeline);
stream.on('[3]', change => { console.log(change.documentKey); });

Drag options to blanks, or click blank then click option'

A'delete'

Bwatch

Cchange

D'insert'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'insert' instead of 'delete' filters the wrong operation.

Using other event names than 'change' will not capture change events.

Using methods other than watch() will not create a change stream.

This code watches for 'delete' operations, starts the change stream with watch(), and listens for 'change' events to log the document key.