AggregateVersion

Marks a field or property as containing the aggregate version for optimistic concurrency control.

The aggregate version is used to ensure that commands are applied to the correct version of an aggregate, preventing concurrent modification conflicts. This is essential in distributed systems where multiple clients might attempt to modify the same aggregate simultaneously.

The annotated field/property should contain an integer representing the current version of the aggregate. The framework automatically increments this version when events are applied.

Example usage:

@AggregateRoot
class OrderAggregate(
    @AggregateId
    val orderId: String,

    @AggregateVersion
    var version: Int = 0
) {

    @OnCommand
    fun updateOrder(command: UpdateOrderCommand): OrderUpdated {
        // Version will be checked automatically before applying changes
        return OrderUpdated(orderId, command.updates)
    }

    @OnEvent
    fun onUpdated(event: OrderUpdated) {
        version++ // Version incremented after event application
    }
}

See also