如何在 Drools 5 中匹配多个相同类型的对象？

Question

鉴于内存中有两个或更多 BMSContract 对象的集合，我需要使用 BMSContract.status 字段匹配特定模式。如果在此类集合中只有一个且只有一个 BMSCContract 的状态为 ACTIVE，我的规则应该解析为 Success。对象和状态代码的任何其他组合都应解析为失败。同样，此规则仅适用于 2 个或更多对象的集合，并且可以有任意数量：2、5、10、15 或更多。管理单个 BMSCContract 记录的规则集略有不同。这些规则仅适用于多个记录场景，例如：

Case1 - Success
BMSContract(status=ACTIVE)
BMSContract(status=PENDING)
Reason:  only one Active in the collection

Case2 - Success
BMSContract(status=ACTIVE)
BMSContract(status=PENDING)
BMSContract(status=HOLD)
Reason: only one Active in the coll

Case3 - Success
BMSContract(status=ACTIVE)
BMSContract(status=PENDING)
BMSContract(status=HOLD)
BMSContract(status=CANCEL)
Reason:  only one Active in the coll

Case4 - Failure
BMSContract(status=ACTIVE)
BMSContract(status=ACTIVE)
Reason:  too many Active records in coll

Case5 - Failure
BMSContract(status=ACTIVE)
BMSContract(status=ACTIVE)
BMSContract(status=ACTIVE)
Reason:  too many Active records in coll

Case6 - Failure
BMSContract(status=ACTIVE)
BMSContract(status=ACTIVE)
BMSContract(status=ACTIVE)
BMSContract(status=ACTIVE)
BMSContract(status=ACTIVE)
Reason:  too many Active records in coll

Case7 - Failure
BMSContract(status=PENDING)
BMSContract(status=HOLD)
BMSContract(status=OTHER)
Reason:  No Active records in coll

Answer 1

鉴于您有许多 BMSContract 事实，以下规则就足够了：

rule OK
when
  $ac: BMSContract( status == "ACTIVE" )
  not BMSContract( this != $ac, status == "ACTIVE" )
then
  // there is exactly one ACTIVE
end

rule not_OK_1
when
  not BMSContract( status == "ACTIVE" )
then
  // there is no ACTIVE
end

rule not_OK_2
when
  $ac: BMSContract( status == "ACTIVE" )
  exists BMSContract( this != $ac, status == "ACTIVE" )
then
  // there is more than one ACTIVE
end

变体是可能的，如果您需要确定引起问题的事实，可能需要这些变体：

rule not_OK_2a
when
  $ac1: BMSContract( status == "ACTIVE" )
  $ac2: BMSContract( this != $ac, status == "ACTIVE" )
then
  // log and retract $ac2
end