Query filter syntax in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Find documents with age greater than 30

Given a collection users with documents containing an age field, which query returns all users older than 30?

MongoDB

db.users.find({ age: { $gt: 30 } })

A db.users.find({ age: { $gt: 30 } })

B db.users.find({ age: { $lt: 30 } })

C db.users.find({ age: { $gte: 30 } })

D db.users.find({ age: 30 })

💡 Hint

Use $gt to find values greater than a number.

The $gt operator filters documents where the field value is greater than the specified number. $gte includes the number itself, $lt is less than, and matching age: 30 finds exact matches.

❓ query_result

intermediate

Find documents with name starting with 'A'

Which query returns all documents where the name field starts with the letter 'A'?

MongoDB

db.users.find({ name: /^A/ })

A db.users.find({ name: /^A/ })

B db.users.find({ name: { $regex: 'A$' } })

C db.users.find({ name: { $regex: '^A' } })

D db.users.find({ name: { $regex: 'A' } })

💡 Hint

Use a regular expression to match the start of the string.

The regex /^A/ matches strings starting with 'A'. Option A is similar but uses $regex syntax. However, option A is the direct and correct syntax. Option A matches strings ending with 'A'. Option A matches strings containing 'A' anywhere.

📝 Syntax

advanced

Identify the syntax error in this query

Which option contains a syntax error in the MongoDB query filter?

MongoDB

db.products.find({ price: { $lt: 100, $gt: 50 } })

A db.products.find({ price: { $gte: 50, $lte: 100 } })

B db.products.find({ price: { $gt: 50, $lt: 100 } })

C db.products.find({ price: { $lt: 100, $gt: 50 } })

D db.products.find({ price: { $lt: 100 } $gt: 50 })

💡 Hint

Check for missing commas or misplaced braces.

Option D is missing a comma between the two operators inside the object, causing a syntax error. Options B, C, and D are syntactically correct.

❓ optimization

advanced

Optimize query to find users with status 'active' or 'pending'

Which query is the most efficient to find users whose status is either 'active' or 'pending'?

MongoDB

db.users.find({ status: { $in: ['active', 'pending'] } })

A db.users.find({ $or: [ { status: 'active' }, { status: 'pending' } ] })

B db.users.find({ status: 'active' || 'pending' })

C db.users.find({ status: { $in: ['active', 'pending'] } })

D db.users.find({ status: { $or: ['active', 'pending'] } })

💡 Hint

Use $in operator for multiple possible values in one field.

Option C uses $in which is optimized for matching any value in the list. Option C works but is less concise. Option C is invalid syntax. Option C uses $or incorrectly inside a field.

🧠 Conceptual

expert

Understanding query filter behavior with missing fields

What will the query db.orders.find({ shippedDate: { $exists: false } }) return?

A Documents where the shippedDate field exists and is null

B Documents where the shippedDate field does not exist

C Documents where the shippedDate field is missing or null

D Documents where the shippedDate field exists and has any value

💡 Hint

The $exists operator checks if a field is present in the document.

The query with $exists: false returns documents where the field is not present at all. It does not include documents where the field exists but is null.