Buses

DomusJS includes three core buses to implement CQRS and event-driven architectures:

✅ Command Bus → Handles actions that change state.
✅ Query Bus → Handles data retrieval requests.
✅ Event Bus → Publishes and distributes domain events.

These buses provide clean separation between application concerns and make it easy to extend or swap implementations.

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Command Bus

What It Does

• Dispatches commands to their corresponding handlers.
• Used for operations that change system state.

Default Implementation

The infrastructure module ships with InMemoryCommandBus, which uses tsyringe to resolve handlers.

const commandBus = container.resolve<CommandBus>('CommandBus');
await commandBus.dispatch(new CreateUserCommand(...));

Custom Implementations

You can swap in your own implementation (e.g., using RabbitMQ):

container.register<CommandBus>('CommandBus', { useClass: RabbitMQCommandBus });

✅ As long as it follows the CommandBus interface, it integrates smoothly.

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Query Bus

What It Does

• Handles read-only operations.
• Returns data without modifying system state.

Default Implementation

The InMemoryQueryBus is provided by default:

const queryBus = container.resolve<QueryBus>('QueryBus');
const user = await queryBus.ask(new GetUserByIdQuery(userId));

Custom Implementations

You can create wrappers (e.g., for caching, logging) or distributed setups:

container.register<QueryBus>('QueryBus', { useClass: DistributedQueryBus });

✅ This makes reads scalable and modular.

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Event Bus

What It Does

• Publishes domain events to subscribed handlers.
• Enables decoupled, reactive architectures.

Default Implementation

The InMemoryEventBus works out of the box for synchronous, in-process eventing.

const eventBus = container.resolve<EventBus>('EventBus');
await eventBus.publish([new UserRegisteredEvent(...) ]);

Provided Distributed Implementations

DomusJS already includes ready-to-use implementations for distributed eventing:

✅ RabbitMQ → RabbitMQEventBus
✅ Google Pub/Sub → GooglePubSubEventBus

To use them, simply register them inside your registerDomusCore() call:

registerDomusCore({
  eventBus: new RabbitMQEventBus(), // or GooglePubSubEventBus
});

✅ This enables cross-service event propagation for microservice architectures.

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Best Practices

✅ Register all buses via registerDomusCore() or by overriding afterwards.
✅ Keep command, query, and event flows separate for clarity.
✅ Use middleware patterns (logging, metrics, tracing) around bus executions.
✅ For microservices, use distributed buses to communicate across services.