Arrays in documents in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

MongoDB

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

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

A"mongodb"

B{ "$in": ["mongodb"] }

C{ "$all": ["mongodb"] }

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

Attempts:

3 left

💡 Hint

Common Mistakes

Using $in or $all unnecessarily when a direct value works.

Using incorrect query operators that don't match the array content.

To find documents where the array contains a specific value, you can directly query with that value. Here, 'tags: "mongodb"' matches documents where 'tags' array includes 'mongodb'.

2fill in blank

medium

Complete the code to find documents where the 'scores' array contains at least one value greater than 80.

MongoDB

db.collection.find({ scores: { [1]: 80 } })

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

A$gt

B$lt

C$eq

D$ne

Attempts:

3 left

💡 Hint

Common Mistakes

Using $lt which means 'less than' instead of 'greater than'.

Using $eq which checks for equality, not greater than.

The operator $gt means 'greater than'. So, this query finds documents where the 'scores' array has at least one element greater than 80.

3fill in blank

hard

Fix the error in the query to find documents where the 'comments' array contains an object with 'author' equal to 'Alice'.

MongoDB

db.collection.find({ comments: { [1]: { author: "Alice" } } })

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

A$size

B$in

C$all

D$elemMatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using $in which matches values but not objects by fields.

Using $all which requires all conditions to be met by array elements.

The $elemMatch operator matches documents where at least one element in the array matches the specified query. Here, it finds documents with a 'comments' array containing an object with 'author' equal to 'Alice'.

4fill in blank

hard

Fill both blanks to find documents where the 'ratings' array has exactly 3 elements and contains the value 5.

MongoDB

db.collection.find({ ratings: { [1]: 3, [2]: [5] } })

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

A$size

B$eq

C$in

D$gt

Attempts:

3 left

💡 Hint

Common Mistakes

Using $eq instead of $in to check for value presence in array.

Using $gt which checks for greater than, not array length.

$size checks the array length, so $size: 3 means the array has exactly 3 elements. $in checks if the array contains the value 5.

5fill in blank

hard

Fill all three blanks to create a query that finds documents where the 'reviews' array contains an object with 'score' greater than 7 and 'verified' equal to true.

MongoDB

db.collection.find({ reviews: { [1]: { score: { [2]: 7 }, verified: { [3]: true } } } })

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

A$elemMatch

B$gt

Cverified

D$eq

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'verified' as a key inside $elemMatch without $eq operator.

Using $in or $all instead of $elemMatch for object matching.

$elemMatch matches array elements by multiple conditions. Inside it, $gt checks if 'score' is greater than 7, and $eq checks if 'verified' is true.