Change stream events (insert, update, delete) in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Identify the change stream event type for a document insertion

Given a MongoDB change stream watching a collection, what is the value of the operationType field in the event document when a new document is inserted?

A "update"

B "delete"

C "insert"

D "replace"

💡 Hint

Think about what the event type would be when a new document is added.

When a new document is added to a collection, the change stream event's operationType is "insert".

❓ query_result

intermediate

Determine the change stream event for a document deletion

What is the operationType value in a MongoDB change stream event when a document is deleted from a collection?

A "delete"

B "drop"

C "insert"

D "update"

💡 Hint

Consider the event type that signals removal of a document.

The operationType for a deletion event in a change stream is "delete".

📝 Syntax

advanced

Which change stream event document contains the updated fields?

In a MongoDB change stream event for an update operation, which field contains the changed fields and their new values?

A "documentKey"

B "updateDescription.updatedFields"

C "fullDocument"

D "ns"

💡 Hint

Look for the field that describes what changed inside the document.

The updateDescription.updatedFields field contains the fields that were changed and their new values in an update event.

🧠 Conceptual

advanced

Understanding the difference between 'replace' and 'update' events

Which statement correctly describes the difference between a 'replace' and an 'update' operationType in MongoDB change streams?

A 'replace' means the entire document was replaced; 'update' means only some fields changed

B 'replace' means the document was deleted; 'update' means the document was inserted

C 'replace' and 'update' are synonyms and mean the same thing

D 'replace' means the collection was dropped; 'update' means the document was replaced

💡 Hint

Think about whether the whole document or just parts of it changed.

A 'replace' event means the entire document was replaced with a new one, while an 'update' event means only some fields were changed.

🔧 Debug

expert

Identify the error in this change stream pipeline

You want to watch only delete events on a collection using a change stream with this pipeline:

[ { $match: { operationType: "delete" } } ]

But your code throws an error. What is the most likely cause?

MongoDB

const pipeline = [ { $match: { operationType: "delete" } } ];
const changeStream = collection.watch(pipeline);

A The 'operationType' field should be matched as a number, not a string

B The pipeline must use '$match' with 'fullDocument' instead of 'operationType'

C The 'operationType' field must be inside 'updateDescription' in the match stage

D The pipeline is correct; the error is likely from missing permissions or connection issues

💡 Hint

Check if the pipeline syntax matches MongoDB documentation for filtering by operationType.

Filtering by 'operationType' in the $match stage is valid syntax. Errors usually come from permissions or connection problems, not the pipeline itself.