wow-api/me.ahoo.wow.api.annotation/OnError

OnError

@Target(allowedTargets = [AnnotationTarget.FUNCTION, AnnotationTarget.ANNOTATION_CLASS])

@OnMessage(functionKind = FunctionKind.ERROR, defaultFunctionName = "onError")

annotation class OnError

Marks a function as a command error handler within an aggregate.

Functions annotated with @OnError are invoked when command processing fails. They provide an opportunity to handle errors gracefully, potentially recovering from failures or publishing error events for monitoring and debugging.

Error handlers can:

Log error details for monitoring
Publish error events for external systems
Attempt error recovery or compensation
Transform exceptions into domain events
Trigger fallback business logic

Error handlers receive the original command and the exception that occurred, allowing for context-aware error processing.

Example usage:

@AggregateRoot
class OrderAggregate {

    @OnCommand
    fun create(command: CreateOrderCommand): OrderCreated {
        // Command processing that might fail
        validateOrder(command)
        return OrderCreated(command.orderId, command.items)
    }

    @OnError
    fun onCreateError(command: CreateOrderCommand, error: Exception): OrderCreationFailed? {
        // Log the error
        logger.error("Failed to create order ${command.orderId}", error)

        // Publish error event for monitoring
        return if (error is ValidationException) {
            OrderCreationFailed(command.orderId, error.message ?: "Validation failed")
        } else null // Don't publish events for unexpected errors
    }
}

OnError

See also