轴突框架: only first event is applied during command handler

Question

我正在尝试创建一个命令处理程序，将命令视为多个子命令。每个子命令都会生成一个事件(然后该事件应该更新聚合的状态)。每个子命令的处理依赖于最新的聚合状态(来自前一个子命令)。

例如，考虑以下聚合:

package axon.poc

import org.axonframework.commandhandling.CommandHandler
import org.axonframework.eventsourcing.EventSourcingHandler
import org.axonframework.modelling.command.AggregateIdentifier
import org.axonframework.modelling.command.AggregateLifecycle
import org.axonframework.spring.stereotype.Aggregate
import org.slf4j.LoggerFactory
import java.util.UUID

@Aggregate
class Aggregate() {

    companion object {
        private val logger = LoggerFactory.getLogger(Aggregate::class.java)
    }

    @AggregateIdentifier
    internal var aggregateId: UUID? = null

    private var value: Int = 0

    @CommandHandler
    constructor(command: Command): this() {
        logger.info("generating create event")
        var applyMore = AggregateLifecycle.apply(CreatedEvent(command.aggregateId))
        for (i in 0 until command.value) {
            applyMore = applyMore.andThenApply {
                logger.info("generating update event: ${value+1}")
                UpdatedEvent(command.aggregateId, value+1)
            }
        }
        logger.info("completed command handler")
    }

    @EventSourcingHandler
    fun on(event: CreatedEvent) {
        logger.info("event sourcing handler: $event")
        this.aggregateId = event.aggregateId
        this.value = 0
    }

    @EventSourcingHandler
    fun on(event: UpdatedEvent) {
        logger.info("event sourcing handler: $event")
        this.value = event.value
    }

}

当此代码处理 Command(value = 2) 时，它会生成

[main] INFO org.axonframework.spring.stereotype.Aggregate - generating create event
[main] INFO org.axonframework.spring.stereotype.Aggregate - completed command handler
[main] INFO org.axonframework.spring.stereotype.Aggregate - event sourcing handler: CreatedEvent(aggregateId=65a7a461-61bb-451f-b2d9-8460994eeb1a)
[main] INFO org.axonframework.spring.stereotype.Aggregate - generating update event: 1
[main] INFO org.axonframework.spring.stereotype.Aggregate - generating update event: 1
[main] INFO org.axonframework.spring.stereotype.Aggregate - event sourcing handler: UpdatedEvent(aggregateId=65a7a461-61bb-451f-b2d9-8460994eeb1a, value=1)
[main] INFO org.axonframework.spring.stereotype.Aggregate - event sourcing handler: UpdatedEvent(aggregateId=65a7a461-61bb-451f-b2d9-8460994eeb1a, value=1)

在执行 applyMore 之前正在处理第一个事件 (CreatedEvent)。但是，即使 applyMore 已链接，UpdatedEvent 也不会由事件源处理程序处理，直到两者都生成为止。

我期待(并希望):

[main] INFO org.axonframework.spring.stereotype.Aggregate - generating create event
[main] INFO org.axonframework.spring.stereotype.Aggregate - completed command handler
[main] INFO org.axonframework.spring.stereotype.Aggregate - event sourcing handler: CreatedEvent(aggregateId=65a7a461-61bb-451f-b2d9-8460994eeb1a)
[main] INFO org.axonframework.spring.stereotype.Aggregate - generating update event: 1
[main] INFO org.axonframework.spring.stereotype.Aggregate - event sourcing handler: UpdatedEvent(aggregateId=65a7a461-61bb-451f-b2d9-8460994eeb1a, value=1)
[main] INFO org.axonframework.spring.stereotype.Aggregate - generating update event: 2
[main] INFO org.axonframework.spring.stereotype.Aggregate - event sourcing handler: UpdatedEvent(aggregateId=65a7a461-61bb-451f-b2d9-8460994eeb1a, value=2)

这是 Axon 的错误吗？或者我是否误解了应该如何使用它？如何原子地处理多个“命令”？ IE。全部通过或全部失败。

Answer 1

TLDR;这是一个错误。

您遇到了一种仅发生在构造函数中的非常具体的情况。从 Axon 的角度来看，挑战在于您需要一个实例来应用事件。但是，该实例仅在构造函数完成后才可用。

andThenApply 函数正是为此目的而提供的(并且您正确使用了它)。但是，在您的情况下，代码(错误地)评估得太早了。我必须在本地运行您的代码并进行调试，以找出到底发生了什么。

根本原因是 AnnotatedAggregate 的 andThenApply 实现调用 apply，而不是 publish。前者将看到它当前正在执行延迟的任务，并安排在这些任务结束时实际发布。下一个任务执行相同的操作。因此，这两个事件最终都会先创建，然后在创建后发布。

您是否有兴趣将此问题作为问题提交到 Axon issue tracker 中？ ？这样，积分就会到达它们所属的地方。