OnEvent

Marks a function as a domain event handler.

Functions annotated with @OnEvent are invoked when domain events are published. They allow aggregates to react to events from the same or different aggregates, enabling complex business workflows and state synchronization.

Event handlers are used for:

• Updating aggregate state based on events

• Implementing event sourcing within aggregates

• Cross-aggregate communication and coordination

• Maintaining derived state and projections

Example usage:

@EventProcessor
class OrderEventProcessor {

    @OnEvent
    fun onOrderCreated(event: OrderCreated) {
        // Update inventory
        inventoryService.reserveItems(event.items)

        // Send confirmation email
        emailService.sendOrderConfirmation(event.customerId, event.orderId)
    }

    @OnEvent
    fun onOrderShipped(event: OrderShipped) {
        // Update shipping records
        shippingService.recordShipment(event.orderId, event.trackingNumber)
    }
}

Parameters

See also