How to use the planning entity difficulty in the local search phase? - optaplanner

Question

I'm trying to sort the planning entities on decreasing difficulty in the local search phase.
I tried to add the "entitySelector" in the config file like the following but it results in a ConversionException:
<localSearch>
<termination>
<maximumUnimprovedStepCount>500</maximumUnimprovedStepCount>
</termination>
<moveListFactory>
<cacheType>PHASE</cacheType> <!-- STEP, PHASE -->
<selectionOrder>RANDOM</selectionOrder>
<moveListFactoryClass>com.abcdl.be.solver.move.factory.ParentChangeMoveFactory</moveListFactoryClass>
<entitySelector>
<cacheType>PHASE</cacheType>
<selectionOrder>SORTED</selectionOrder>
<sorterManner>DECREASING_DIFFICULTY</sorterManner>
</entitySelector>
</moveListFactory>
<acceptor>
<lateAcceptanceSize>400</lateAcceptanceSize>
<entityTabuSize>5</entityTabuSize>
</acceptor>
<forager>
<pickEarlyType>NEVER</pickEarlyType> <!-- FIRST_BEST_SCORE_IMPROVING -->
<acceptedCountLimit>3</acceptedCountLimit>
</forager>
</localSearch>
The following Comparator class in annotated on the domain model :
public class NodeDifficultyComparator implements Comparator<Node>{
public int compare(Node a, Node b) {
return new CompareToBuilder()
.append(a.getResources(), b.getResources()) // the most difficult nodes are the ones who use the most resources
.append(a.getId(), b.getId())
.toComparison();
}
}
Did I choose a wrong placement for the "entitySelector" tag ? Should I do this in an another way ??
Thanks for your help.

Answer 1

Implementation detail: the element <moveListFactory> is defined by the class MoveListFactoryConfig. If you look at the source of that class, it does not have a field called entitySelector, so you cannot nest an <entitySelector> element in it.
There are 2 ways to solve your problem:
Instead of using <moveListFactory>, use <changeMoveSelector>, which does support an <entitySelector> element. You can then delete your custom ParentChangeMoveFactory class. The <changeMoveSelector> has many advantages over a custom MoveListFactory, such as JIT support and much more.
If you have a good reason to have a custom MoveListFactory (for example due to some complex reasons which move filtering can't cover), then adjust your ParentChangeMoveFactory to sort the entity list before generating the moves. Remember to shallow clone that list first, as you don't want your sorting to affect the entity list references by the workingSolution instance. The point is: if you write a custom MoveListFactory you're in total control on how to generate the moves, but you do need to do everything yourself...