Optaplanner: Iterate over list variable in drools rule file - drools

Question

I am solving a problem similar to employee rostering. I have an additional constraint. The employees have a "type" value assigned to them. It's a hard constraint that atleast 1 employee of each "type" be there everyday. I have modelled it as follows:
rule "All employee types must be covered"
when
$type: Constants.EmployeeType() from Constants.EmployeeType.values()
not Shift(employeeId != null, $employee: getEmployee(), $employee.getType() == $type.getValue())
then
scoreHolder.addHardConstraintMatch(kcontext, -100);
end
This rule however, does not consider that the constraint be satisfied on each day. I have a list of date strings. How can I iterate over them in the drools file in the same manner that I am on the EmployeeType enum?
Edit: I figured out a way but it feels like a hack. When initialising the list of date strings, I also assign it to a static variable. Then I am able to use the static variable similar to the enum.
rule "All employee types must be covered"
when
$type: Constants.EmployeeType() from Constants.EmployeeType.values()
$date: String() from Constants.dateStringList;
not Shift(employeeId != null, $date == getDate(), $employee: getEmployee(), $employee.getType() == $type.getValue())
then
scoreHolder.addHardConstraintMatch(kcontext, -100);
end
Don't think this is the correct approach though.

Answer 1

Your approach works, but having to define dynamic configurations in a static property of a class doesn't sound right (like you pointed out).
One solution would be to either use a global in the session, or to have a fact class that specify this configuration.
Using a global
If you decide to take this approach, then you need to define a global of type List<String> in your DRL and then use it in your rules in combination with the memberOf operator:
global List<String> dates;
rule "All employee types must be covered"
when
$type: Constants.EmployeeType() from Constants.EmployeeType.values()
not Shift(
employeeId != null,
date memberOf dates,
$employee: getEmployee(),
$employee.getType() == $type.getValue()
)
then
scoreHolder.addHardConstraintMatch(kcontext, -100);
end
It is recommended to set the value for global before you insert any fact Shift into you session:
List<String> dates = //get the List from somewhere
ksession.setGlobal("dates", dates);
Using a Fact Class
Other than a global, you can model your configuration as a class. This makes things easier if you want for example to modify the configuration inside the rules themselves.
for this approach you will need to have a class containing the List<String> first. You could in theory insert the List<String> without wrapping it in any class, but this will make things hard to read and maintain.
public class DatesConfiguration {
private List<String> dates;
//... getters + setters
}
Then, you need to instantiate an object of this class and to insert it into your session:
DatesConfiguration dc = new DatesConfiguration();
dc.setDates(...);
ksession.insert(dc);
At this point, the object you have created is just another fact for Drools and can be used in your rules:
rule "All employee types must be covered"
when
$type: Constants.EmployeeType() from Constants.EmployeeType.values()
DatesConfiguration($dates: dates)
not Shift(
employeeId != null,
date memberOf $dates,
$employee: getEmployee(),
$employee.getType() == $type.getValue()
)
then
scoreHolder.addHardConstraintMatch(kcontext, -100);
end
Hope it helps,