MongoDB — Transactions

Basic Transaction

const session = client.startSession();
session.startTransaction();

try {
  db.orders.insertOne({ userId: ObjectId("..."), total: 100 }, { session });
  db.inventory.updateOne({ _id: ObjectId("...") }, { $inc: { stock: -1 } }, { session });
  
  session.commitTransaction();
} catch (error) {
  session.abortTransaction();
} finally {
  session.endSession();
}

Transaction Requirements

Requirement	Description
Replica set	Required for transactions
Storage engine	WiredTiger
Time limit	60 seconds default

Retry Logic

const session = client.startSession();

for (let retry = 0; retry < 3; retry++) {
  try {
    session.startTransaction();
    // Operations
    await session.commitTransaction();
    break;
  } catch (error) {
    if (error.errorCode === 112) { // WriteConflict
      continue;
    }
    throw error;
  }
}

Mini Practice

1. Start a transaction
2. Commit transaction
3. Abort transaction
4. Add retry logic

Up Next

Continue with Validation — document validation.