Transport & Patterns — Series 3

Preview — 3 of 10 questions

Why the async form rather than register?

javascript

ClientsModule.registerAsync([
  {
    name: 'ORDERS_SERVICE',
    imports: [ConfigModule],
    inject: [ConfigService],
    useFactory: (c: ConfigService) => ({
      transport: Transport.RMQ,
      options: { urls: [c.getOrThrow<string>('RABBITMQ_URL')], queue: 'orders' },
    }),
  },
]);

ABecause register cannot configure the RabbitMQ transport

BThe options come from a factory resolved through the container, so the broker URL is read from validated configuration rather than captured from process.env while the module's metadata was first evaluated — which happens before any .env file has been loaded

CBecause the async form connects lazily and the synchronous one connects eagerly

DBecause only the async form allows more than one client per module

What does @Ctx() provide?

javascript

@EventPattern('order.created')
handle(@Payload() data: OrderCreated, @Ctx() context: RmqContext) {}

AThe Nest execution context, with getHandler() and getClass()

BThe application's configuration for the current transport

CA per-message request-scoped store

DThe transport-specific context object — for RabbitMQ the channel and the original message, for Kafka the topic, partition and offset — which is what manual acknowledgement, offset commits and header access all need

Does this match?

javascript

// producer
client.send({ cmd: 'sum', version: 1 }, [1, 2, 3]);
// consumer
@MessagePattern({ cmd: 'sum' })
sum(@Payload() data: number[]) {}

ANo — object patterns are compared by their serialised form, so { cmd: 'sum', version: 1 } and { cmd: 'sum' } are different patterns and no handler matches

BYes, because cmd matches and extra keys are ignored

CYes, because object patterns are matched by partial containment

DNo, because object patterns are unsupported — only strings may be used

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