I want to have a nested exists in my rule, but when I run it I get a mismatched input error. I am trying to find if, for an object with 2 lists, there exists an object in list 1 and an an object in list 2 such that they are equivalent.

Here are the relevant objects:

public class A {
  List<B> bList;
  List<C> cList;
}

public class B {
  String name;
}

public class C {
  String id;
}

(B == C if B.name == C.id)

Is there a Drools-only solution or workaround for what I want to do?

Here is my rule (causes mismatched input error).

rule "find B-C match"

when
$a: A(bList != null && cList != null)
  exists $b: B(
    exists $c: C($b.name == $c.id)
    from $a.cList)
  from $a.bList
then
System.out.println("A has a match");
// do other stuff
end