Pipeline execution order matters in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start an aggregation pipeline with a match stage filtering documents where age is greater than 25.

MongoDB

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

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

Amatch

Bgroup

Csort

Dproject

Attempts:

3 left

💡 Hint

Common Mistakes

Using $group instead of $match will cause an error because grouping requires a different structure.

Using $sort or $project here won't filter documents.

The $match stage filters documents based on the given condition. Here, it selects users older than 25.

2fill in blank

medium

Complete the code to sort the documents by score in descending order after filtering.

MongoDB

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

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Aproject

Bgroup

Csort

Dlimit

Attempts:

3 left

💡 Hint

Common Mistakes

Using $group instead of $sort will aggregate documents, not order them.

Using $limit will restrict the number of documents but not sort them.

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

3fill in blank

hard

Fix the error in the pipeline by placing the $project stage correctly to include only name and score fields.

MongoDB

db.users.aggregate([ { $[1]: { score: { $gt: 50 } } }, { $project: { name: 1, score: 1 } } ])

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

Agroup

Bmatch

Csort

Dlimit

Attempts:

3 left

💡 Hint

Common Mistakes

Placing $match after $project can cause unexpected results or errors.

Using $group here is incorrect because we want to filter, not aggregate.

The $match stage should come before $project to filter documents before selecting fields.

4fill in blank

hard

Fill both blanks to correctly filter active users and then group them by city counting the number of users per city.

MongoDB

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

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

Amatch

Bproject

Cgroup

Dsort

Attempts:

3 left

💡 Hint

Common Mistakes

Using $project instead of $match will not filter documents.

Using $sort instead of $group will not aggregate counts.

First, $match filters active users. Then, $group groups by city and counts users.

5fill in blank

hard

Fill all three blanks to filter users older than 30, sort by age ascending, and project only name and age fields.

MongoDB

db.users.aggregate([ { $[1]: { age: { $gt: 30 } } }, { $[2]: { age: 1 } }, { $[3]: { name: 1, age: 1, _id: 0 } } ])

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

Amatch

Bsort

Cproject

Dgroup

Attempts:

3 left

💡 Hint

Common Mistakes

Changing the order of stages can lead to wrong results.

Using $group instead of $project will aggregate instead of selecting fields.

The pipeline first filters with $match, then sorts with $sort, and finally selects fields with $project.