Gather the domain objects in a planning solution

A TimeTable wraps all Timeslot, Room, and Lesson instances of a single dataset. Furthermore, because it contains all lessons, each with a specific planning variable state, it is a planning solution and it has a score:

  • If lessons are still unassigned, then it is an uninitialized solution, for example, a solution with the score -4init/0hard/0soft.

  • If it breaks hard constraints, then it is an infeasible solution, for example, a solution with the score -2hard/-3soft.

  • If it adheres to all hard constraints, then it is a feasible solution, for example, a solution with the score 0hard/-7soft.

Create the src/main/java/org/acme/schooltimetabling/domain/TimeTable.java class:

package org.acme.schooltimetabling.domain;

import java.util.List;

import ai.timefold.solver.core.api.domain.solution.PlanningEntityCollectionProperty;
import ai.timefold.solver.core.api.domain.solution.PlanningScore;
import ai.timefold.solver.core.api.domain.solution.PlanningSolution;
import ai.timefold.solver.core.api.domain.solution.ProblemFactCollectionProperty;
import ai.timefold.solver.core.api.domain.valuerange.ValueRangeProvider;
import ai.timefold.solver.core.api.score.buildin.hardsoft.HardSoftScore;

@PlanningSolution
public class TimeTable {

    @ValueRangeProvider
    @ProblemFactCollectionProperty
    private List<Timeslot> timeslotList;
    @ValueRangeProvider
    @ProblemFactCollectionProperty
    private List<Room> roomList;
    @PlanningEntityCollectionProperty
    private List<Lesson> lessonList;

    @PlanningScore
    private HardSoftScore score;

    public TimeTable() {
    }

    public TimeTable(List<Timeslot> timeslotList, List<Room> roomList, List<Lesson> lessonList) {
        this.timeslotList = timeslotList;
        this.roomList = roomList;
        this.lessonList = lessonList;
    }

    public List<Timeslot> getTimeslotList() {
        return timeslotList;
    }

    public List<Room> getRoomList() {
        return roomList;
    }

    public List<Lesson> getLessonList() {
        return lessonList;
    }

    public HardSoftScore getScore() {
        return score;
    }

}

The TimeTable class has an @PlanningSolution annotation, so Timefold knows that this class contains all of the input and output data.

Specifically, this class is the input of the problem:

  • A timeslotList field with all time slots

    • This is a list of problem facts, because they do not change during solving.

  • A roomList field with all rooms

    • This is a list of problem facts, because they do not change during solving.

  • A lessonList field with all lessons

    • This is a list of planning entities, because they change during solving.

    • Of each Lesson:

      • The values of the timeslot and room fields are typically still null, so unassigned. They are planning variables.

      • The other fields, such as subject, teacher and studentGroup, are filled in. These fields are problem properties.

However, this class is also the output of the solution:

  • A lessonList field for which each Lesson instance has non-null timeslot and room fields after solving

  • A score field that represents the quality of the output solution, for example, 0hard/-5soft

The value range providers

The timeslotList field is a value range provider. It holds the Timeslot instances which Timefold can pick from to assign to the timeslot field of Lesson instances. The timeslotList field has an @ValueRangeProvider annotation to connect the @PlanningVariable with the @ValueRangeProvider, by matching the type of the planning variable with the type returned by the value range provider.

Following the same logic, the roomList field also has an @ValueRangeProvider annotation.

The problem fact and planning entity properties

Furthermore, Timefold needs to know which Lesson instances it can change as well as how to retrieve the Timeslot and Room instances used for score calculation by your TimeTableConstraintProvider.

The timeslotList and roomList fields have an @ProblemFactCollectionProperty annotation, so your TimeTableConstraintProvider can select from those instances.

The lessonList has an @PlanningEntityCollectionProperty annotation, so Timefold can change them during solving and your TimeTableConstraintProvider can select from those too.