nestjs / TypeOrm database transaction

Question

Assuming we have 2 services, A and B. Service A has a function doing the following:

1. Validate the data
2. Call a service B function, that makes changes to

Answer 1

Here is how I solved it since I needed to use a pessimistic lock.

I feel it is the "Nest" way of doing things as you can simply ask NestJS to inject an instance of a Typeorm Connection and you're good to go.

@Injectable()
class MyService {
  // 1. Inject the Typeorm Connection
  constructor(@InjectConnection() private connection: Connection) { }

  async findById(id: number): Promise {
    return new Promise(resolve => {
      // 2. Do your business logic
      this.connection.transaction(async entityManager => {
        resolve(
          await entityManager.findOne(Thing, id, {
            lock: { mode: 'pessimistic_write' },
          }),
        );
      });
    });
  }
}

Simply place whatever other logic you need inside the .transaction block and you're good to go.

NOTE: You MUST use the entityManager provided by the .transaction method or else it will not work.