Change streams on collections in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to watch changes on the 'users' collection.

MongoDB

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

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

Aobserve

Bwatch

Clisten

Dsubscribe

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'listen' or 'observe' which are not valid MongoDB methods.

Trying to use 'subscribe' which is not a MongoDB collection method.

The watch() method starts a change stream on the collection.

2fill in blank

medium

Complete the code to specify the pipeline to filter change events for inserts only.

MongoDB

const pipeline = [ { $match: { 'operationType': [1] } } ];

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

A'insert'

B'update'

C'delete'

D'replace'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'update' which watches for modifications, not inserts.

Using 'delete' which watches for removals.

The operationType 'insert' filters events to only new document insertions.

3fill in blank

hard

Fix the error in the code to correctly iterate over change events.

MongoDB

for await (const change of changeStream.[1]()) {
  console.log(change);
}

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

Anext

Biterator

Ccursor

Dstream

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'next' which is a method on the cursor, not the changeStream itself.

Using 'stream' or 'iterator' which are not valid methods here.

The cursor() method returns an async iterator over the change stream events.

4fill in blank

hard

Fill both blanks to create a change stream with a pipeline filtering for deletes and fullDocument lookup.

MongoDB

const changeStream = db.collection('orders').watch([1], { fullDocument: [2] });

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

A[{ $match: { operationType: 'delete' } }]

Btrue

Cfalse

D[{ $match: { operationType: 'insert' } }]

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong operationType in the pipeline.

Setting fullDocument to false which disables full document lookup.

The pipeline filters for 'delete' operations, and fullDocument: true returns the full document on change.

5fill in blank

hard

Fill all three blanks to handle change events and close the stream on error.

MongoDB

try {
  for await (const change of changeStream.[1]()) {
    console.log(change.[2]);
  }
} catch (error) {
  console.error(error);
  changeStream.[3]();
}

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

Acursor

BfullDocument

Cclose

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'next' instead of 'cursor()' for iteration.

Accessing 'document' instead of 'fullDocument'.

Not closing the stream on error.

Use cursor() to iterate, access fullDocument for changed data, and close() to stop the stream on error.