Change stream pipelines for filtering in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a change stream pipeline in MongoDB?

A change stream pipeline is a sequence of stages that filters and transforms change events from a MongoDB collection or database before they are returned to the application.

beginner

How do you filter change events by operation type using a change stream pipeline?

You use a $match stage in the pipeline to specify the operationType field, for example: { $match: { operationType: 'insert' } } to get only insert events.

intermediate

Why use change stream pipelines for filtering instead of filtering in application code?

Filtering in the pipeline reduces the amount of data sent over the network and lowers application processing, making the system more efficient and responsive.

intermediate

Can you filter change streams by fields inside the changed document?

Yes, you can use $match to filter on fields inside the fullDocument or updateDescription fields, for example: { $match: { 'fullDocument.status': 'active' } }.

beginner

What MongoDB aggregation stage is commonly used in change stream pipelines for filtering?

The $match stage is commonly used to filter change events based on criteria like operationType or document fields.

Which aggregation stage is used to filter change events in a MongoDB change stream pipeline?

A $project

B $group

C $match

D $sort

The $match stage filters documents based on specified conditions, making it ideal for filtering change events.

How would you filter a change stream to only receive 'update' operations?

A { $match: { operationType: 'update' } }

B { $match: { operationType: 'insert' } }

C { $match: { fullDocument: 'update' } }

D { $match: { updateDescription: 'update' } }

Filtering by operationType with value 'update' returns only update events.

What is a benefit of filtering change streams using pipelines?

A Reduces network traffic and processing load

B Increases the number of events received

C Delays event delivery

D Requires more application code

Filtering early reduces unnecessary data sent and processed.

Can you filter change streams by a field inside the changed document?

A No, filtering is not supported

B No, only operationType can be filtered

C Yes, but only on _id field

D Yes, using $match on fullDocument fields

You can filter on any field inside fullDocument using $match.

Which of these is NOT a valid operationType to filter in change streams?

A delete

B modify

C insert

D replace

'modify' is not a valid operationType; valid types include insert, update, delete, replace, etc.

Explain how to use a change stream pipeline to filter only insert operations in MongoDB.

Think about filtering events by their type using $match.

Describe why filtering change streams at the pipeline level is better than filtering in application code.

Consider network and processing costs.