Use cases for change streams in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Primary use case of MongoDB change streams

Which of the following is the main purpose of using change streams in MongoDB?

A To track real-time changes in the database and react immediately

B To perform batch updates on large collections

C To create backups of the database automatically

D To optimize query performance by indexing

💡 Hint

Think about how applications can respond instantly to data changes.

Change streams allow applications to listen for real-time changes in MongoDB collections and databases, enabling immediate reactions to inserts, updates, deletes, and more.

❓ query_result

intermediate

Output of a change stream watching insert operations

Given a change stream watching only insert operations on a collection, what will be the output when a new document is inserted?

MongoDB

db.collection.watch([{ $match: { operationType: 'insert' } }])

A A document describing the deleted document with operationType 'delete'

B An error because operationType 'insert' is invalid

C No output because change streams do not track inserts

D A document describing the inserted document with operationType 'insert'

💡 Hint

Consider what operationType 'insert' means in change streams.

When watching for inserts, the change stream outputs documents describing each inserted document with operationType set to 'insert'.

📝 Syntax

advanced

Correct syntax to watch changes on a database

Which of the following is the correct syntax to open a change stream on an entire MongoDB database?

A db.watch()

B db.getMongo().watch()

C db.getSiblingDB('mydb').watch()

D db.getMongo().getDB('mydb').watch()

💡 Hint

Think about how to access a database object and then call watch on it.

To watch changes on a database, you must get the database object and call watch() on it. The correct way is db.getSiblingDB('mydb').watch().

❓ optimization

advanced

Optimizing change stream filters

To reduce the amount of data your application processes, which approach optimizes change stream usage best?

A Use a $match stage in the change stream pipeline to filter only needed operation types

B Fetch all changes and filter them in the application code

C Use change streams without any filters to get all changes

D Disable change streams and poll the database every minute

💡 Hint

Filtering early reduces unnecessary data transfer and processing.

Using a $match stage in the change stream pipeline filters changes at the database level, reducing network and processing load.

🧠 Conceptual

expert

Use case best suited for MongoDB change streams

Which scenario is best suited for implementing MongoDB change streams?

A Running complex aggregation queries on large datasets periodically

B Building a real-time notification system that alerts users when their data changes

C Archiving old data to cold storage every month

D Creating indexes to speed up read queries

💡 Hint

Change streams are designed for real-time data change tracking.

Change streams enable applications to react instantly to data changes, making them ideal for real-time notifications.