Watch method for real-time updates in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start watching changes on the collection.

MongoDB

const changeStream = collection.[1]();

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

Asubscribe

Blisten

Cobserve

Dwatch

Attempts:

3 left

💡 Hint

Common Mistakes

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

The watch() method starts a change stream to listen for real-time updates on 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);
});

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Adata

Bchange

Cevent

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'update' which is a type of change but not the event name.

The 'change' event is emitted when a change occurs in the watched collection.

3fill in blank

hard

Fix the error in the code to properly close the change stream when done.

MongoDB

await changeStream.[1]();

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Aclose

Bend

Cstop

Dterminate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'stop' or 'end' which are not valid methods on change streams.

The close() method properly closes the change stream to release resources.

4fill in blank

hard

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

MongoDB

const pipeline = [
  { $match: { 'operationType': [1] } }
];
const changeStream = collection.watch(pipeline, { [2]: false });

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A'insert'

BfullDocument

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'true' for fullDocument disables filtering, or wrong operationType string.

The pipeline filters for 'insert' operations only. The option fullDocument: false disables returning the full changed document.

5fill in blank

hard

Fill all three blanks to create a change stream that watches updates and prints the updated fields.

MongoDB

const pipeline = [
  { $match: { 'operationType': [1] } }
];
const changeStream = collection.watch(pipeline);
changeStream.on('[2]', change => {
  console.log(change.updateDescription.[3]);
});

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

A'update'

B'change'

CupdatedFields

DremovedFields

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'removedFields' instead of 'updatedFields' when printing changes.

The pipeline filters for 'update' operations. The event listened to is 'change'. The updatedFields property shows which fields were changed.