MongoDB Study Guide 2026
Everything you need to pass the MongoDB exam in one place: the exam format, every topic to study, real practice questions with explanations, flashcards, and full-length practice tests. Free, no sign-up needed.
📋 MongoDB Exam Format at a Glance
📚 MongoDB Topics to Study (36)
✍️ Sample MongoDB Questions & Answers
1. What is the ESR rule for compound index design in MongoDB?
The ESR rule states that in a compound index, place Equality fields first, Sort fields second, and Range fields last for optimal query performance.
2. Which field is automatically created by MongoDB for every document if not explicitly provided?
MongoDB automatically creates an _id field for every document if one is not provided. By default, this is an ObjectId — a 12-byte BSON type that encodes a timestamp, machine identifier, process ID, and a random increment, ensuring global uniqueness.
3. What is the impact of using transactions on MongoDB performance?
Multi-document transactions in MongoDB introduce overhead: they hold locks, create larger oplog entries, and require coordination across members. MongoDB documentation recommends using the document model to avoid transactions where possible and to keep transactions short when they are necessary.
4. What is the correct way to sort query results in descending order by a field named 'score'?
Using -1 as the sort value specifies descending order, while 1 specifies ascending order.
5. What is the $addFields stage used for in aggregation?
$addFields outputs documents containing all existing fields plus any newly added or modified fields.
6. What is a write conflict in a MongoDB transaction?
A write conflict occurs when two concurrent transactions attempt to write to the same document. MongoDB detects this and aborts one of the conflicting transactions with a TransientTransactionError, expecting the application to retry the aborted transaction.
🎯 Free MongoDB Practice Tests
📖 MongoDB Guides & Articles
What Practice Test Geeks adds beyond an AI chat for MongoDB
An AI chatbot can quiz you, but it can't reproduce the exam conditions or keep your record. Here you get:
- A timed, full-length MongoDB mock exam — 53 questions in 75 minutes with a 70% pass mark, modeled on the official exam's question count and time limit, followed by a score report broken down by exam domain.
- A fixed MongoDB question bank: the same test every attempt, so your score is comparable from one try to the next instead of changing with every regenerated quiz.
- Progress saved on your device: completed tests, scores and missed questions stay in My Progress, so you can retake only what you got wrong.
- A printable MongoDB cheat sheet you can print or save as a PDF.
- MongoDB flashcards built from the same question bank.
- Free MongoDB practice tests with the correct answer shown after each question.
How this page was made: written with AI tools and published by Nathan Beja, founder of Practice Test Geeks, who is responsible for its content. Exam facts are checked against the official sources listed below. Not reviewed by a subject-matter expert. Editorial policy
Sources & references
Exam facts on this page (fees, format, dates, passing scores) are checked against these official sources; the date is our last check. Editorial policy
- 10geneducation.zendesk.com — Test dates, score release, passing score, test delivery, retake policy · verified Oct 2026
- learn.mongodb.com — Eligibility, fees, exam format, time limit · verified Oct 2026