Optaplanner remove customer from working VRP solution

Question

Based on this question i tried the following:

public void doFactChange() {
    Location toBeRemovedLocation = customerToBeRemoved.getLocation();
    Location lookUpWorkingObject = (Location) scoreDirector.lookUpWorkingObject(toBeRemovedLocation);
    scoreDirector.beforeProblemFactRemoved(lookUpWorkingObject);
    routingSolution.getLocationList().remove(lookUpWorkingObject);
    scoreDirector.afterProblemFactRemoved(lookUpWorkingObject);
    Customer workingCustomer = (Customer) scoreDirector.lookUpWorkingObject(customerToBeRemoved);

    for (Customer customer : routingSolution.getCustomerList()) {
        while (customer != null) {
            if (customer == workingCustomer) {
                if (customer.getPreviousStandstill() != null) {
                    scoreDirector.beforeVariableChanged(customer, "previousStandstill");
                    customer.getPreviousStandstill().setNextCustomer(customer.getNextCustomer());

                    scoreDirector.afterVariableChanged(customer, "previousStandstill");
                }

                scoreDirector.beforeVariableChanged(customer, "nextCustomer");
                customer.getNextCustomer().setPreviousStandstill(customer.getPreviousStandstill());
                scoreDirector.afterVariableChanged(customer, "nextCustomer");
            }
            customer = customer.getNextCustomer();
        }
    }

    scoreDirector.beforeEntityRemoved(workingCustomer);
    routingSolution.getCustomerList().remove(workingCustomer);
    scoreDirector.afterEntityRemoved(workingCustomer);
    scoreDirector.triggerVariableListeners();
}

Note: customerToBeRemoved is an instance object that's created before calling doFactChange()

But I received the following exception even before calling scoreDirector.triggerVariableListeners

java.lang.IllegalStateException: The entity (Customer--9048381398840634905) has a variable (previousStandstill) with value (Customer--9070671076516032025) which has a sourceVariableName variable (nextCustomer) with a value (Customer-8518512081385427431) which is not that entity. Verify the consistency of your input problem for that sourceVariableName variable.

Another question:

I tried to remove the entity directly as follows:

public void doFactChange() {
    Location toBeRemovedLocation = customerToBeRemoved.getLocation();
    Location lookUpWorkingObject = (Location) scoreDirector.lookUpWorkingObject(toBeRemovedLocation);
    scoreDirector.beforeProblemFactRemoved(lookUpWorkingObject);
    routingSolution.getLocationList().remove(lookUpWorkingObject);
    scoreDirector.afterProblemFactRemoved(lookUpWorkingObject);
    Customer workingCustomer = (Customer) scoreDirector.lookUpWorkingObject(customerToBeRemoved);

    scoreDirector.beforeEntityRemoved(workingCustomer);
    routingSolution.getCustomerList().remove(workingCustomer);
    scoreDirector.afterEntityRemoved(workingCustomer);
    scoreDirector.triggerVariableListeners();
}

Is that valid?

Answer 1

This method works fine with optaplanner VRP example using easy, incremental and drl score calculators:

public void removeRandomCustomer()
{
    doProblemFactChange(scoreDirector -> {
        VehicleRoutingSolution solution = scoreDirector.getWorkingSolution();
        int rnd = 4; //select a random customer
        if (solution.getCustomerList().size() > rnd)
        {
            Customer customer = solution.getCustomerList().get(rnd);
            scoreDirector.beforeEntityRemoved(customer);
            removeCustomer(solution, customer);
            scoreDirector.afterEntityRemoved(customer);
            scoreDirector.triggerVariableListeners();
        }
    });
}

private void removeCustomer(VehicleRoutingSolution solution, Customer customer)
{
    Standstill anchor = customer.getPreviousStandstill();
    Customer nextCustomer = customer.getNextCustomer();
    //anchor shouldn't be null in an initialized solution
    if (anchor != null)
        anchor.setNextCustomer(nextCustomer);
    if (nextCustomer != null)
        nextCustomer.setPreviousStandstill(anchor);
    solution.getCustomerList().remove(customer);
}

Edit:

Alternative approach for shadow variables with easy/incremental scoring:

private void removeCustomer(ScoreDirector<VehicleRoutingSolution> scoreDirector, VehicleRoutingSolution solution, Customer removeCustomer)
{
    final Customer customer = scoreDirector.lookUpWorkingObject(removeCustomer);
    Standstill anchor = customer.getPreviousStandstill();
    Customer nextCustomer = customer.getNextCustomer();

    //scoreDirector.beforeVariableChanged(anchor, "nextCustomer");
    scoreDirector.beforeVariableChanged(customer, "previousStandstill");    //sets anchor.nextCustomer=null
    customer.setPreviousStandstill(null);
    scoreDirector.afterVariableChanged(customer, "previousStandstill");
    //scoreDirector.afterVariableChanged(anchor, "nextCustomer");
    if(nextCustomer!=null)
    {
        //scoreDirector.beforeVariableChanged(customer, "nextCustomer");
        scoreDirector.beforeVariableChanged(nextCustomer, "previousStandstill");  //sets customer.nextCustomer=null
        nextCustomer.setPreviousStandstill(anchor);
        scoreDirector.afterVariableChanged(nextCustomer, "previousStandstill");
        //scoreDirector.afterVariableChanged(customer, "nextCustomer");
    }

    scoreDirector.beforeEntityRemoved(customer);
    //clone customer list
    ArrayList<Customer> changedList = new ArrayList<>(solution.getCustomerList());
    solution.setCustomerList(changedList);
    solution.getCustomerList().remove(customer);
    scoreDirector.afterEntityRemoved(customer);
    scoreDirector.triggerVariableListeners();  //sets customer.vehicle=null, sets all nextCustomer.vehicle=null

}

The solution should be in a valid state now but you'll probably have to fix the incremental scoring (easy score is fine because doProblemFactChange() recalculates it automatically), perhaps by removing the retraction in VehicleRoutingIncrementalScoreCalculator.beforeEntityRemoved(). If everything else fails you could first move the customer to the end of the chain and remove it from there.