$elemMatch for complex array queries in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find documents where the 'scores' array has an element greater than 80.

MongoDB

db.students.find({ scores: { [1]: { score: { $gt: 80 } } } })

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

A$and

B$gt

C$elemMatch

D$in

Attempts:

3 left

💡 Hint

Common Mistakes

Using $gt directly on the array field instead of inside $elemMatch.

Using $in which checks for exact values, not conditions.

The $elemMatch operator matches documents that contain an array field with at least one element that matches all the specified query criteria.

2fill in blank

medium

Complete the code to find documents where the 'grades' array has an element with 'score' greater than 85 and 'type' equal to 'exam'.

MongoDB

db.records.find({ grades: { $elemMatch: { score: { [1]: 85 }, type: 'exam' } } })

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.

Using $eq which means equal to.

The $gt operator means 'greater than'. Here it checks if the 'score' field in any element is greater than 85.

3fill in blank

hard

Fix the error in the query to find documents where 'items' array has an element with 'price' less than 50 and 'qty' greater than 10.

MongoDB

db.orders.find({ items: { [1]: { price: { $lt: 50 }, qty: { $gt: 10 } } } })

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

A$and

B$or

C$all

D$elemMatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using $and or $or directly on the array field instead of $elemMatch.

Using $all which matches all elements but not conditions inside elements.

The $elemMatch operator is needed to match documents where an array element satisfies multiple conditions together.

4fill in blank

hard

Fill both blanks to find documents where 'reviews' array has an element with 'rating' at least 4 and 'verified' is true.

MongoDB

db.products.find({ reviews: { [1]: { rating: { [2]: 4 }, verified: true } } })

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

A$elemMatch

B$gte

C$lt

D$ne

Attempts:

3 left

💡 Hint

Common Mistakes

Using $lt instead of $gte for rating condition.

Using $ne which means not equal.

$elemMatch matches array elements with multiple conditions. $gte means 'greater than or equal to', used here for rating at least 4.

5fill in blank

hard

Fill all three blanks to find documents where 'logs' array has an element with 'status' equal to 'error', 'code' greater than 500, and 'retry' false.

MongoDB

db.system.find({ logs: { [1]: { status: [2], code: { [3]: 500 }, retry: false } } })

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

A$elemMatch

B'error'

C$gt

D'success'

Attempts:

3 left

💡 Hint

Common Mistakes

Using $and instead of $elemMatch.

Using 'success' instead of 'error' for status.

Using $lt instead of $gt for code.

$elemMatch matches array elements with multiple conditions. The status must be the string 'error'. The code must be greater than 500 using $gt.