I’m assigning rooms to lessons in my schedule generator. My current model looks like this:

@PlanningEntity
class Lesson {
    ...
    @PlanningVariable(allowsUnassigned = true)
    Room room;

    Set<String> requiredRoomAttributes;
    ...
}

class Room {
    Set<String> attributes;
}

However, I need to change it so that each lesson can have an arbitrary (but fixed) number of rooms. (In the user interface the user can specify that a lesson 3 rooms with three different set of required attributes.)

(A @PlanningListVariable does not seem suitable here since each room can be assigned to multiple lessons as long as the lessons don’t collide in time.)

A natural way to model this would be something like:

@PlanningEntity
class Lesson {
    ...
    Set<RoomAssignment> roomAssignments;
    ...
}

class RoomAssignment {
    ...
    Room room; // null until room has been assigned
    Set<String> requiredRoomAttributes;
    ...
}
    
class Room {
    Set<String> attributes;
}

I’m puzzled though because I’m not sure where to put the @PlanningVariable annotation. I assume it must be on the entity, but it’s only the room (not the requiredRoomAttributes that is the actual variable).

This leads me to believe that this is a better modelling:

@PlanningEntity
class Lesson {
    ...
    @PlanningVariable
    List<Room> rooms;

    // The i:th set represents the requirements for the i:th room
    List<Set<String>> requiredAttributes;
    ...
}

class Room {
    Set<String> attributes;
}

Question 1: Is this the recommended way to model this problem, or is there a better way?

Question 2: Is there any chance any built in move selector could be used to update individual elements in List<Room> rooms, or should I go ahead and write custom move selectors?

Question 3: Correct me if I’m wrong, but I feel like Timefold internally probably could handle an arbitrary (but fixed) list of independent variables. Has this ever been considered? For example something like:

@PlanningEntity
class Lesson {
    @PlanningVariableArray
    Room[] rooms = new Room[10];
}