CODEWITHSUNDEEP
javaoptaplannerdomain-model
Radical
Radical

Reputation: 1073

OptaPlanner domain modelling - multiple PlanningEntity classes?

I am trying to construct the domain model for an optimization use-case, using OptaPlanner. In my mind the following problem should be modeled using two @PlanningEntity classes, but since the OptaPlanner documentation often argues that you usually only need one @PlanningEntity class, I am wondering if I am modelling my problem incorrectly, or whether this is in fact a situation to have two @PlanningEntity classes.

Consider a school timetabling problem like the example provided by OptaPlanner here, but imagine we are also planning and optimising which students attend a lesson. If these problems are independent, then this could be solved by writing two different solvers, and running the "student planner" solver first, and then the "schedule planner" solver. However, assume that these two are not independent. For example, constraints regarding the placement of students in certain lessons might interact with when these lessons take place (student X prefers lessons in the morning, student Y prefers lessons in the afternoon, and student Z cannot have two lessons directly in a row). So, when optimising, I would like the solver to be able to consider both the timeslot of lessons as well as the students attending a lesson.

My idea to model this would be to extend the TimeTable class in the example with a second @PlanningEntity modelling student to lesson assignments, and in the Lesson class the studentGroup field would be replaced with a list containing all the students assigned to that lesson, probably in the form of a shadow variable (though this is an implementation detail).

  1. Am I correct in that in the above example, two different @PlanningEntity classes ("Student to lesson assignment" as well as Lesson) are appropriate? Or is there a way to model this problem using only a single @PlanningEntity? I know that a @PlanningVariable cannot be a list, so I assume a List<Student> students planning variable is not possible.
  2. Am I correct that a @PlanningEntityCollection can only be a field on the @PlanningSolution? Or is there a way to have the student assignments be a field on the Lesson?

Upvotes: 0

Views: 238

Answers (1)

Radovan Synek
Radovan Synek

Reputation: 1029

Since you want to assign lessons to time and rooms and students to lessons, I think you truly need two @PlanningEntity classes. As multiple students can attend multiple lessons, you can perhaps create a new StudentAssignment @PlanningEntity class with Lesson as its @PlanningVariable.

Yes, the @PlanningEntityCollection can only be a field on the @PlanningSolution class. What can be put inside the @PlanningEntity class is the @ValueRangeProvider that provides values for the @PlanningVariable field.

Upvotes: 0

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