如何从轴突框架中的聚合成员访问聚合根状态

Question

Suppose I have CloudServer Aggregate which has cloudService as a member of it. If the users want to upgrade their cloudService I need to calculate if they have enough balance to do so, but I don't know how can I access balance state of AggregateRoot from AggregateMember. Here's how the code looks like.

@Aggregate
class CloudServerAggregate() {
  @AggregateIdentifier
  lateinit var cloudServerId: String
  lateinit var balance: BigDecimal

  @AggregateMember(eventForwardingMode = ForwardMatchingInstances::class)
  var cloudService = mutableListOf<CloudService>()
}

class CloudService(
  @EntityId
  val serviceId: String
) {

  val isActivated: false
  
  @CommandHandler
  fun handle(command: UpgradeServiceCommand){
//    I need to check the current balance of this cloud server, but I also need to use the state inside this class
//    if(balance < command.price) {
//      throw IllegalArgumentException("Insufficient balance")
//    }
//    if(!isActivated){
//      throw IllegalArgumentException("Some errors")
//    }
  }
}

Answer 1

There is no direct way of accessing aggregate from the aggregate members.

Since action you want to do is depended from aggregate root, it would be best that you move the command handler to the aggregate itself.

Check the balance and upgrade service accordingly. You could even call "command handler" function directly on service object from aggregate root's command handler, if balance passes validation.

Answer 2

There should be a way by extending AnnotatedAggregate. Then you should be able to use getAggregateRoot() (or aggregateRoot with kotlin) and then cast with 'as CloudServerAggregate'.