Unit of Work Pattern: Batch Database Changes in a Single Transaction

Multiple repository calls in a single use case each open their own database connection/transaction. Either all changes should commit together or none should, but individual repositories cannot coordinate.

A Unit of Work object wraps a transaction and exposes repositories that all operate within it. Commit or rollback the entire batch at the end.

interface UnitOfWork {
  users: UserRepository;
  orders: OrderRepository;
  commit(): Promise<void>;
  rollback(): Promise<void>;
}

class PrismaUnitOfWork implements UnitOfWork {
  users: UserRepository;
  orders: OrderRepository;
  private tx: PrismaTransaction;

  constructor(prisma: PrismaClient) {
    this.tx = prisma; // simplified; real impl wraps $transaction
    this.users = new PrismaUserRepository(this.tx);
    this.orders = new PrismaOrderRepository(this.tx);
  }

  async commit() { /* commit tx */ }
  async rollback() { /* rollback tx */ }
}

// Use case
async function placeOrder(uow: UnitOfWork, userId: string, items: Item[]) {
  const user = await uow.users.findById(userId);
  const order = Order.create(user!, items);
  await uow.orders.save(order);
  await uow.users.save(user!.deductCredits(order.total));
  await uow.commit();
}

Unit of Work ensures atomicity across multiple repository operations that logically belong to the same business transaction, preventing partial updates that corrupt data integrity.