如何在OptaPlanner中添加约束一辆车只能在一个方向上go？

Question

• Each employee has a direction in which he works.
• Each car can travel in one direction. If an employee who works in direction A was added to the car, then only employees who work in the same direction should be in it

@PlanningEntity
public class Employee {

    @PlanningId
    private Long id;

    private String direction;

    @PlanningVariable(valueRangeProviderRefs = "vehicleRange")
    private Vehicle vehicle;

}

@PlanningEntity
public class Vehicle {

    @PlanningId
    private Long id;

    @InverseRelationShadowVariable(sourceVariableName = "vehicle")
    List<Employee> employees = new ArrayList<>();

    private String direction;

}

What is the best constraint for this?

Answer 1

Since the car's direction is not builtin but defined by the first passenger, I'd go with an instance variable.

• When the car is instantiated, it's direction is not set (=null).
• When adding the first passenger check the direction of the car
  • If it is null, the car's direction is set to the passengers' direction and the passenger is added.
  • If it is non-null, compare the passenger's direction with the car's direction.
    • If directions match, add the passenger.
    • If no match, reject the passenger.
• When removing passengers, check if the car is now empty. If it is empty, change the direction to null.

That would allow you to reuse a car once the passengers have left.

Answer 2

I think I have found a solution.

private Constraint directionConflict(ConstraintFactory factory) {
    return factory.forEach(Employee.class)
        .groupBy(Employee::getVehicle)
        .filter(vehicle -> vehicle.getEmployees().stream()
            .anyMatch(employee -> !Objects.equals(employee.getDirection(),
                vehicle.getEmployees().get(0).getDirection())))
        .penalize("Direction conflict", HardMediumSoftLongScore.ONE_HARD);
}