Optaplanner: Can we use two planning variables with (nullable = true)?

Question

Can we use two planning variables with (nullable = true) for each of them?

If so, how can we deal with them in the Drools rule file?

I know that when we use one planning variable we define it with (nullable = true) and then in the rule we use $planningVariable != null as in the " pas " example, I tried this and it worked well, but what about using two planning variables?

Can we apply this on the curriculumCourse ? and if so, the over constrained data should appear in the output as unassigned for the two planning variables or appear in only one of them?

Answer 1

Yes, of course you can. But as usual, you 'll have to make sure your score constraints (= score rules) penalize/reward what you want to achieve.

For example on CurriculumCourse, I presume you 'd have a negative medium constraint that penalizes a Lecture if either room or period is null . If both are null , don't penalize it more, or you'll end up with a lot semi assigned entities. But despite that, you'll still probably end up with a few semi assigned entities, so to fix that:

• Either do some post-processing to make all those not assigned at all (= both vars null ) as a semi-assignment is useless.
• Or add a hard constraint against semi assignments to avoid them entirely (even in intermediate solution states).

Additional solving efficiently can be gained from:

• A ChangeMove selector that moves both room and period, as changing just one to/from null will never yield a better solution.