Pipeline mental model (stages flow) in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start an aggregation pipeline with the first stage.

MongoDB

db.collection.aggregate([ { [1]: { age: { $gt: 25 } } } ])

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

A$match

B$group

C$sort

D$project

Attempts:

3 left

💡 Hint

Common Mistakes

Using $group as the first stage without filtering.

Using $sort before filtering documents.

The $match stage filters documents to pass only those that match the condition. It is usually the first stage in a pipeline.

2fill in blank

medium

Complete the code to add a stage that groups documents by 'department' and counts them.

MongoDB

db.collection.aggregate([ { $match: { status: 'active' } }, { [1]: { _id: "$department", count: { $sum: 1 } } } ])

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

A$project

B$group

C$sort

D$limit

Attempts:

3 left

💡 Hint

Common Mistakes

Using $project instead of $group for grouping.

Trying to count documents in $match stage.

The $group stage groups documents by a specified key and can perform accumulations like counting.

3fill in blank

hard

Fix the error in the pipeline stage that sorts documents by 'score' descending.

MongoDB

db.collection.aggregate([ { $match: { active: true } }, { [1]: { score: -1 } } ])

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

A$sort

B$limit

C$match

D$group

Attempts:

3 left

💡 Hint

Common Mistakes

Using $group or $match instead of $sort for ordering.

Using positive 1 for descending order.

The $sort stage orders documents by specified fields. Using $sort with { score: -1 } sorts descending by score.

4fill in blank

hard

Fill both blanks to project only the 'name' and 'total' fields in the output.

MongoDB

db.collection.aggregate([ { $match: { status: 'complete' } }, { [1]: [2] } ])

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

A$project

B{ name: 1, total: 1 }

C{ name: 0, total: 0 }

D$group

Attempts:

3 left

💡 Hint

Common Mistakes

Using $group instead of $project to select fields.

Setting fields to 0 to include them.

The $project stage selects which fields to include or exclude. Using { name: 1, total: 1 } includes only those fields.

5fill in blank

hard

Fill all three blanks to create a pipeline that filters active users, groups by city counting users, and sorts by count descending.

MongoDB

db.users.aggregate([ { [1]: { active: true } }, { [2]: { _id: "$city", userCount: { $sum: 1 } } }, { [3]: { userCount: -1 } } ])

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

A$match

B$group

C$sort

D$project

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing the order of stages.

Using $project instead of $group for counting.

This pipeline first filters active users with $match, then groups them by city counting users with $group, and finally sorts the results by userCount descending with $sort.