Sparse indexes in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a sparse index on the field "email".

MongoDB

db.users.createIndex({ email: 1 }, { [1]: true })

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

Asparse

Bbackground

Cunique

DexpireAfterSeconds

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'unique' instead of 'sparse' causes errors if duplicates exist.

Omitting the sparse option creates a normal index including all documents.

The sparse option creates an index that only includes documents where the indexed field exists.

2fill in blank

medium

Complete the code to find documents where the "phone" field exists using the sparse index.

MongoDB

db.contacts.find({ [1]: { $exists: true } })

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

Aphone

Bemail

Caddress

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Querying on a different field than the sparse index.

Using $exists: false instead of true.

To use the sparse index on the phone field, query documents where phone exists.

3fill in blank

hard

Fix the error in the code to create a sparse index on "username".

MongoDB

db.accounts.createIndex({ username: 1 }, { [1]: true })

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

Aunique

BexpireAfterSeconds

Cbackground

Dsparse

Attempts:

3 left

💡 Hint

Common Mistakes

Using string 'true' instead of boolean true.

Using an unrelated option name.

The sparse option must be a boolean true, not a string.

4fill in blank

hard

Fill both blanks to create an index on "profile.age" and make it run in the background.

MongoDB

db.users.createIndex({ [1]: 1 }, { [2]: true })

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

Aprofile.age

Bsparse

Cbackground

Dunique

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'sparse' instead of 'background' for the second option.

Using 'unique' which is unrelated here.

Use profile.age as the field and background: true to create the index without blocking operations.

5fill in blank

hard

Fill all three blanks to create a sparse, unique index on "email" with background creation.

MongoDB

db.customers.createIndex({ [1]: 1 }, { [2]: true, [3]: true, [4]: true })

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

Aemail

Bunique

Csparse

Dbackground

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing sparse and unique options.

Omitting background option.

This creates an index on email that is both unique and sparse, running in the background.