OPTAPLANNER: Add function of planning entities as optimization constraint

Question

I want to add a function of the list of planning entities as a constraint. More specifically, each planning entity has a contribution x, and I want to implement a constraint that adds a HARD score if the sum of all the x contributions is greater than X. Something like...

Constraint ConstraintX(ConstraintFactory constraintFactory) {
    return constraintFactory
            .forEach(planningEntity.class)
            .filter(planningEntity-> planningEntity.get_x())
            .sum().penalize("Sum of xs bigger than X", 
                            HardMediumSoftScore.ONE_HARD,
                            sum > X # what goes here???                                                
                            );
}

Answer 1

See OptaPlanner documentation on Constraint Collectors . Specifically ConstraintCollectors.sum(...) does exactly what you need.