Multikey indexes for arrays in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a multikey index on the 'tags' array field.

MongoDB

db.articles.createIndex({ tags: [1] })

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

A"text"

B-1

C1

D"hashed"

Attempts:

3 left

💡 Hint

Common Mistakes

Using -1 instead of 1 creates a descending index but still works; however, 1 is standard.

Using 'text' or 'hashed' is for different index types, not multikey.

To create a multikey index on an array field, use 1 for ascending order on the array field.

2fill in blank

medium

Complete the code to find documents where the 'tags' array contains 'mongodb'.

MongoDB

db.articles.find({ tags: [1] })

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

A{ $all: ["mongodb"] }

B"mongodb"

C{ $elemMatch: { $eq: "mongodb" } }

D{ $in: ["mongodb"] }

Attempts:

3 left

💡 Hint

Common Mistakes

Using $all or $in works but is more complex than needed for a single value.

Using $elemMatch is unnecessary for a simple equality check.

To find documents where an array contains a specific value, you can directly query with the value.

3fill in blank

hard

Fix the error in the index creation code to correctly create a multikey index on 'comments.author'.

MongoDB

db.posts.createIndex({ [1]: 1 })

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

A"comments_authors"

B"author"

C"comments"

D"comments.author"

Attempts:

3 left

💡 Hint

Common Mistakes

Indexing just 'comments' creates an index on the array but not on the nested field.

Using 'author' alone misses the array context.

Using 'comments_authors' is not a valid field name.

To create a multikey index on a field inside an array of subdocuments, use the dot notation 'comments.author'.

4fill in blank

hard

Fill both blanks to create a compound multikey index on 'tags' and 'comments.author'.

MongoDB

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

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

A"tags"

B"comments.author"

C"author"

D"comments"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'author' alone misses the array context.

Using 'comments' alone does not index the nested field.

Mixing up field names causes errors.

Compound multikey indexes can be created on multiple array fields using their correct field names.

5fill in blank

hard

Fill all three blanks to create a multikey index on 'categories', 'tags', and 'comments.author'.

MongoDB

db.blog.createIndex({ [1]: 1, [2]: 1, [3]: 1 })

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

A"categories"

B"tags"

C"comments.author"

D"author"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'author' alone instead of 'comments.author'.

Omitting any array field from the index.

Using incorrect field names.

To index multiple array fields, list each with 1 for ascending order using their full field names.