Setting global variables in working memory in Drools planner - drools

Question

How do I add a global variable to working memory in drools planner's solver to be able to use in scores drool. This is similar to https://issues.jboss.org/browse/JBRULES-2700 but couldn't find a solution though.

Answer 1

What you might be looking for is a #ProblemFactProperty.
Quoting from the documentation:
All objects returned by those [annotated] methods will be inserted into the
ConstraintStreams or Drools session, so the constraint steams or score
rules can access them.
In my own words: You can hold a reference to your global object in your #PlanningSolution class. If you annotate its getter with #ProblemFactProperty you can access it from your drools file.

Answer 2

First some preaching: Using a service (set as a global) to calculate part of the score will break delta based score calculation (read the manual section on that topic), resulting in much less score calculations per second (say 50 instead of 5000 per second on big data sets).
Then a HACK solution: In the StartingSolutionInitializer (soon known as CustomSolverPhaseCommand) do solverScope.getWorkingMemory().setGlobal("key", value).
Then a real, long-term solution: Could you motivate why you need to be able to do this? We can think about adding support for this with something like an optional WorkingMemoryPreperator.

Answer 3

After set the planningProblem:
solver.setPlanningProblem(planningProblem);
You can get access the workingMemory via solutionDirector(HACK) :
DefaultSolutionDirector solutionDirector = ((DefaultSolver)solver).getSolverScope().getSolutionDirector();
solutionDirector.getWorkingMemory().setGlobal("list", new ArrayList<String>());
Cheers!

Answer 4

If you need to use some helper methods in the planner rules, try the following approach which I used in my project:
Create a utility class which includes the helper methods.
Import the utility class in the rule file like importing it in a java class.
Use the helper method in the rule. If you want to use a helper method in the condition, wrap using eval(). If you want to use a helper method in the then part, just use it as normal java method call.
For example, say you have a utility class named PlanningUtil like below:
public class PlanningUtil {
public boolean isGood() {return true;}
public void doSomething() {//...}
}
Then import the utility class in the rule file,
import PlanningUtil;
Use the utility method in the rule
rule "MyRule"
when
eval(PlanningUtil.isGood())
then
PlanningUtil.doSomething(); // note the ';' is a must.
end