Joiner construction

[jerome1968]

Hello, I would appreciate some advice on the modelling of the following constraint.
I have resources (crude carriers) that are carrying crude oil to large vessels (VLCC). In order t satisfy the demand from the vessel, I have to sum all the volumes (of a given oil classification) brought by all the candidate crude carriers until the vessel location in the route.
In the code below, I use a joiner that joins the vessel with demand (the facts) and the carriers that are candidate to serve that vessel. In the joiner, instead of b.getDestinateVLCC(), I would like to write something like that: b.getCandidateVLCC(a.getVlcc()) where this method will returns the vessel object itself (to perform the join sucessfully) or null depending on the capability between the two ships. Unfortunately, this not allowed in the joiner construction. If I don´t want to use the ship capability profile, is there a way to sum the quantities of all crude carriers without using any joiner?

    private Constraint demand(@NonNull ConstraintFactory constraintFactory) {
        return constraintFactory.forEach(VLCCDemand.class)
                .join(CrudeCarrier.class, equal(a -> a.getVlcc(), b -> b.getDestinateVLCC()))
                .groupBy((vlccDemand,crudeCarrier) -> vlccDemand.getDemand(),
                        sum((vlccDemand,crudeCarrier) ->
                                crudeCarrier.totalVolume(vlccDemand.getVlcc().getLocation(),
                                        vlccDemand.getDemand().getClassification())))
                .filter((demand, volume) -> volume < demand.getVolume())
                .penalize(HardSoftLongScore.ONE_HARD, (demand, volume) -> (int)(demand.getVolume() - volume))
                .asConstraint("VLCC demand");
    }

[triceo]

Hello @jerome1968!

You should look into Joiners.filtering(...) - it allows you to use any boolean expression. It doesn't carry the full indexing performance of the equals joiner, but sometimes it's what's necessary.

[jerome1968]

Thank you @triceo for your advice, which addresses my issue.

[Christopher-Chianelli]

Welcome @jerome1968 !

From what I read of this issue, b.getCandidateVLCC(a.getVlcc()) seems to be an object expression, not a boolean expression. Are you attempting to group by b.getCandidateVLCC(a.getVlcc()) , or are you filtering by a property of b.getCandidateVLCC(a.getVlcc()) (i.e. something like b.getCandidateVLCC(a.getVlcc()) != null). If you want to group by the expression, you can add it as a group key:

    private Constraint demand(@NonNull ConstraintFactory constraintFactory) {
        return constraintFactory.forEach(VLCCDemand.class)
                .join(CrudeCarrier.class, equal(a -> a.getVlcc(), b -> b.getDestinateVLCC()))
                // expand is used to avoid recomputation
                .expand((vlccDemand,crudeCarrier)  -> crudeCarrier.getCandidateVLCC(vlccDemand.getVlcc()))
                // I am assuming null vessels are not wanted
                .filter((vlccDemand, crudeCarrier, vessel) -> vessel != null)
                .groupBy((vlccDemand,crudeCarrier, vessel) -> vlccDemand.getDemand(),
                        (vlccDemand,crudeCarrier, vessel) -> vessel,
                        sum((vlccDemand,crudeCarrier, vessel) ->
                                crudeCarrier.totalVolume(vlccDemand.getVlcc().getLocation(),
                                        vlccDemand.getDemand().getClassification())))
                .filter((demand, vessel, volume) -> volume < demand.getVolume())
                .penalize(HardSoftLongScore.ONE_HARD, (demand, vessel volume) -> (int)(demand.getVolume() - volume))
                .asConstraint("VLCC demand");
    }

If you want to filter by a property, either use Joiners.filtering or add an intermediate filter operation.

[jerome1968]

Thank you @Christopher-Chianelli for your complete response. At the end, I filter by a property using Joiners.filtering.