Multi-Document Transactions

MongoDB supports ACID transactions across multiple documents and collections, similar to a relational database.

const session = client.startSession();
session.startTransaction();
try {
  await accounts.updateOne({ _id: a }, { $inc: { balance: -100 } }, { session });
  await accounts.updateOne({ _id: b }, { $inc: { balance: 100 } }, { session });
  await session.commitTransaction();
} catch (e) {
  await session.abortTransaction();
}

Tip

Clarify: single-document writes are always atomic by default — multi-document transactions are the newer, opt-in feature (since MongoDB 4.0).