easyinsertOne insertMany
You pass an array of documents to insertMany. By default, one document in the middle fails a unique index check. What happens?
db.users.insertMany([doc1, doc2_dup, doc3])why this works
Built for MongoDB mastery, not memorisation.
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Every MongoDB question shows its code before you answer, so you are reading real MongoDB, not a description of it.
A written explanation, always
Once you attempt a question you get the reasoning, not just a tick. That matters most on MongoDB, where embedding versus referencing, multikey and compound index behaviour, aggregation pipeline stages, read and write concern trade-offs, sharding keys, and replica-set elections.
Your weak topics, named
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faq
Things people ask.
How many MongoDB MCQs are on Journey Uncommon?
589 MongoDB questions right now: 99 easy, 246 medium and 244 hard. That number is read straight from the question table when this page is built, so it is never a rounded marketing figure.
Do I need an account to read the MongoDB questions?
No. Every MongoDB question, including its code snippet, its difficulty and its topic, is readable without signing in. You need a free account only to submit an answer, see which option is correct, and read the worked explanation. We keep it that way so the platform stays honest about what you actually got right.
What do MongoDB interviewers actually test?
Embedding versus referencing, multikey and compound index behaviour, aggregation pipeline stages, read and write concern trade-offs, sharding keys, and replica-set elections.
Which MongoDB topics are covered?
53 distinct topics are tagged on the MongoDB questions, including covered queries internals, WiredTiger storage engine, multikey array indexes, aggregation $match $group, read concern levels, text and $regex search. The topic labels come from the questions themselves, so the list matches what you will actually be asked.
Is MongoDB practice free?
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Where is MongoDB used in real jobs?
Backend roles at document-store shops, analytics pipelines, and teams running Atlas in production.
What a MongoDB question here actually looks like
These are 12 of the 589 MongoDB questions in the library, pulled live from the question table. The snippet, the difficulty and the topic are all here. The answer options and the explanation are not. Those need a free account.
Embedding versus referencing, multikey and compound index behaviour, aggregation pipeline stages, read and write concern trade-offs, sharding keys, and replica-set elections.
Sample MongoDB MCQs
easy$push and $pull
Given { _id: 1, items: [{ k: 'a', n: 1 }, { k: 'b', n: 2 }, { k: 'a', n: 3 }] }, what does $pull: { items: { k: 'a' } } do?
db.col.updateOne({ _id: 1 }, { $pull: { items: { k: 'a' } } })easyfind and query filters
What is the type of the value held in `result` after this line runs?
const result = db.users.find({ active: true });easydocuments and collections
Two documents in the same collection look like this. Is this allowed?
db.people.insertOne({ name: "Ann", age: 30 })
db.people.insertOne({ name: "Bob", city: "NYC", hobbies: ["chess"] })easydeleteOne deleteMany
When deleteOne finds no document matching the filter, what is returned?
db.users.deleteOne({ email: "missing@example.com" })easydeleteOne deleteMany
The collection has 50 documents. What does this command do?
db.logs.deleteMany({})easyfind and query filters
What does find() with an empty filter document return?
db.users.find({})easyupdateOne and $set
What does updateOne do when more than one document matches the filter?
db.orders.updateOne(
{ status: "pending" },
{ $set: { status: "shipped" } }
)easycomparison operators $gt $in
Given documents with a numeric price field, what does this filter match?
db.products.find({ price: { $gt: 100 } })easy_id and ObjectId
What does this code print?
const ObjectId = require("mongodb").ObjectId;
const a = new ObjectId("507f1f77bcf86cd799439011");
const b = new ObjectId("507f1f77bcf86cd799439011");
console.log(a === b);
console.log(a.equals(b));easysort limit skip
Values for score are [50, 90, 70, 20]. Which document's score does this query return first?
db.players.find().sort({ score: -1 }).limit(1)easyprojection include exclude
Given { _id: 1, name: "Ada", age: 30, city: "NYC" }, what is returned?
db.users.find({}, { age: 0, city: 0 })Sign in to answer
Everything above is free to read. Answering needs a free account.
We keep the correct answer, the explanation and the scoring behind sign-in so the platform stays honest, which is why the correct option and the worked explanation for every MongoDB question stay behind a free account. Signing in is free and takes a few seconds.
Where MongoDB shows up
Backend roles at document-store shops, analytics pipelines, and teams running Atlas in production.