How does MongoDB handle transactions and what are the transaction capabilities?

Short answer: MongoDB provides multi-document transactions starting with version 4.0. This allows you to execute multiple operations in a transaction, ensuring ACID properties (Atomicity, Consistency, Isolation, Durability) across multiple documents and collections.

Example code

const session = client.startSession(); try { session.startTransaction(); db.collection1.updateOne({ _id: 1 }, { $set: { status: "completed" } }, { session }); db.collection2.updateOne({ _id: 2 }, { $set: { status: "shipped" } }, { session }); session.commitTransaction(); } catch (error) { session.abortTransaction(); } finally { session.endSession(); }

Real-world example (ShopNest)

Checkout wraps stock decrement + order insert in a transaction so you never sell stock you do not have.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.