How should a TypeORM transaction work?

Definition:

A transaction groups database changes so they can commit together or roll back together. In TypeORM, the transaction callback receives a manager tied to that transaction's connection. Queries issued through an unrelated global repository may not participate, even if they appear inside the same JavaScript callback.

Key points:

• Put related writes inside one transaction.

• Use the provided transaction manager for every query in that transaction.

• Let failures roll back; avoid slow external API calls while holding locks.

• Choose a concurrency strategy as well as a transaction boundary; atomicity alone does not prevent every race.

Example — transaction context:

// dataSource, Order and OrderAudit are configured application objects.
await dataSource.transaction(async manager => {
  const order = await manager.save(Order, { status: 'created' });
  await manager.save(OrderAudit, { orderId: order.id, action: 'created' });
});

• Both writes use the supplied manager. An uncaught failure prevents the transaction from committing either write.

Interview point:

• Explain which exact writes belong together and demonstrate that each uses the transaction manager.