[rules-users] DRL Pattern match to subclass?

[Kris Nuttycombe]

Hi, all,

I'm trying to figure out a way to perform the following pattern match
in a "when" clause in a drl file. This is with Drools 4.x

I have the following parameterized class (boilerplate omitted):

abstract class Property<T> {
  public String getName() {
      //...
  }

  public abstract T getValue();
}

and subclasses such as

class BigDecimalProperty extends Property<BigDecimal> {
  public BigDecimal getValue() {
    //...
  }
}

I then have an interface as such:

public interface Propertied {
  public Set<Property<?>> getProperties();
}

and an implementing class:

class Plan implements Propertied {
  //...
}

In my rules file, I would like to be able to perform the following
pattern match:

rule "Ensure that plan minimum commitment has been met."
    agenda-group "evaluate-balance"
when
    $plan: Plan()
    $minCommitProperty: BigDecimalProperty(name ==
"minimum_commitment", $minCommitment : value) from $plan.properties
then
    //...
end

Of course, this results in a runtime rule compilation exception
complaining of type mismatch. Is there any better way to encode this
match than to add all properties to the working memory, match the
desired property as a first-class object, then match against the plan
with Plan(properties contains $minCommitProperty)?

Thanks,

Kris