How MongoDB indexes work (B-tree mental model) - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an index on the 'name' field in a MongoDB collection.

MongoDB

db.collection.createIndex({ name: [1] })

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

A1

B-1

C0

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or 2 as index direction, which are invalid.

Confusing ascending (1) with descending (-1).

In MongoDB, creating an index with 1 means ascending order, which is the standard way to index a field.

2fill in blank

medium

Complete the code to find documents where the 'age' field is greater than 25 using an index.

MongoDB

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

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

Alt

Bne

Ceq

Dgt

Attempts:

3 left

💡 Hint

Common Mistakes

Using $lt instead of $gt, which finds smaller values.

Using $eq which looks for exact matches.

The $gt operator means 'greater than', which finds documents with 'age' greater than 25.

3fill in blank

hard

Fix the error in the index creation code to ensure it uses a valid B-tree index on 'score'.

MongoDB

db.collection.createIndex({ score: [1] })

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

A"text"

B2

C1

D"hashed"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2 which is invalid for index direction.

Using 'text' or 'hashed' when a B-tree index is needed.

For a B-tree index, use 1 (ascending) or -1 (descending). Here, 1 is correct. 'text' and 'hashed' create different index types.

4fill in blank

hard

Fill both blanks to create a compound index on 'lastName' ascending and 'age' descending.

MongoDB

db.collection.createIndex({ lastName: [1], age: [2] })

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

A1

B-1

C0

D"text"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 which is invalid for index direction.

Using 'text' which creates a text index, not a B-tree index.

Compound indexes can mix ascending (1) and descending (-1) directions. Here, lastName is ascending, age is descending.

5fill in blank

hard

Fill all three blanks to create a filtered index on 'status' equals 'active' and sort by 'createdAt' descending.

MongoDB

db.collection.createIndex({ status: [1], createdAt: [2] }, { partialFilterExpression: { status: [3] } })

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

A1

B-1

C"active"

D"inactive"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong sort directions.

Using 'inactive' instead of 'active' in the filter.

The index sorts 'status' ascending (1) and 'createdAt' descending (-1). The filter only includes documents where status is 'active'.