Date and timestamp types in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Find documents with dates after 2023-01-01

Given a collection events with a date field of type Date, which query returns all documents where the date is after January 1, 2023?

A db.events.find({ date: { $gt: new Date('2023-01-01') } })

B db.events.find({ date: { $gte: '2023-01-01' } })

C db.events.find({ date: { $gt: ISODate('2023-01-01') } })

D db.events.find({ date: { $gt: '2023-01-01T00:00:00Z' } })

💡 Hint

Use the $gt operator with a Date object to compare dates.

Option A correctly uses new Date() to create a Date object and compares with $gt. Option B compares with a string, which does not work as expected. Option C uses ISODate which is a shell helper and works in the MongoDB shell. Option D compares with a string timestamp, which is not reliable.

🧠 Conceptual

intermediate

Difference between Date and Timestamp types

Which statement correctly describes the difference between MongoDB's Date and Timestamp types?

A <code>Date</code> is deprecated; <code>Timestamp</code> replaces it for all date storage.

B <code>Date</code> stores only date; <code>Timestamp</code> stores date and time.

C <code>Date</code> stores a date and time; <code>Timestamp</code> is for internal replication and stores a time and increment.

D <code>Date</code> stores time in seconds; <code>Timestamp</code> stores time in milliseconds.

💡 Hint

Think about how MongoDB uses Timestamp internally for replication.

Date stores a standard date and time value. Timestamp is a special type used mainly for replication and contains a time and an increment to ensure uniqueness.

📝 Syntax

advanced

Correct syntax to create a Timestamp

Which option correctly creates a MongoDB Timestamp with time 1672531200 and increment 1?

A Timestamp({time: 1672531200, inc: 1})

B Timestamp(1672531200, 1)

C new Timestamp({t: 1672531200, i: 1})

D new Timestamp(1672531200, 1)

💡 Hint

Use the new keyword with two numeric arguments for time and increment.

Option D uses the correct constructor syntax. Option D misses new. Options C and D use invalid argument formats.

❓ optimization

advanced

Efficiently query documents by date range

You want to find all documents in logs collection with createdAt between 2023-01-01 and 2023-01-31. Which query is most efficient assuming createdAt is indexed?

A db.logs.find({ createdAt: { $gte: ISODate('2023-01-01'), $lte: ISODate('2023-01-31') } })

B db.logs.find({ createdAt: { $gte: new Date('2023-01-01'), $lt: new Date('2023-02-01') } })

C db.logs.find({ createdAt: { $gt: new Date('2023-01-01'), $lt: new Date('2023-01-31') } })

D db.logs.find({ createdAt: { $gte: '2023-01-01', $lt: '2023-02-01' } })

💡 Hint

Use inclusive start and exclusive end dates for ranges to avoid overlap.

Option B uses inclusive start and exclusive end with correct Date objects, which is efficient and avoids missing documents on boundary. Option B excludes 2023-01-01 and misses documents on 2023-01-31. Option B uses ISODate which may not be available in all drivers. Option B compares strings, which is less efficient and unreliable.

🔧 Debug

expert

Why does this date query return no results?

Given documents with eventDate stored as Date type, why does this query return no results?

db.events.find({ eventDate: { $eq: '2023-03-15T00:00:00Z' } })

A Because the query compares a string to a Date type, causing no matches.

B Because the date format string is invalid and causes a syntax error.

C Because the field <code>eventDate</code> does not exist in documents.

D Because <code>$eq</code> cannot be used with dates in MongoDB.

💡 Hint

Check the data types used in the query and stored in the documents.

The query compares the eventDate field (a Date object) to a string. MongoDB does not convert types automatically, so no documents match. The correct approach is to compare with a Date object.