Promotion Condition compairing two RAO values

[janbu]

I am currently trying to create a promotion rule that compares two lists in the orderRao object to determine if the rule should be executed anymore. I'm using a RuleIrAttributeRelCondition to achieve this, but it not really works. What is the proper way of doing that?

My code so far:

@Overridepublic RuleIrCondition translate(RuleCompilerContext context,RuleConditionData condition,RuleConditionDefinitionData ruleConditionDefinitionData) {
  var orderRao = context.generateVariable(OrderRAO.class);
  RuleIrAttributeRelCondition maxNumberOfCouponsCondition =
      RuleIrAttributeRelConditionBuilder.newAttributeRelationConditionFor(orderRao)
      .withAttribute("discountValues.size()")
      .withOperator(RuleIrAttributeOperator.LESS_THAN_OR_EQUAL)
      .withTargetAttribute(orderRao)
      .withTargetVariable("coupons.size()")
      .build();
  return maxNumberOfCouponsCondition;
}

Generated Drools rule (part):

when
(
exists (CouponRAO(couponId == "FANCY-COUPON-CODE"))
and
$rao_v5 := OrderRAO(discountValues.size() <= $rao_v5.coupons.size())
)

But the rule is never true...