在Drools和Optaplanner中进行数学运算

Question

我与Drools一起使用optaplanner，并且有Drools规则：

rule "No student double booked"
    when
        ScheduledLesson($timeslot : timeslot, $student : lesson.student)
        ScheduledLesson(timeslot == $timeslot, lesson.student == $student)
    then
        scoreHolder.addHardConstraintMatch(kcontext, -1);
end

这很好。

我想确保学生没有背对背的课程：

rule "Student does not have contiguous lessons"
    when
        ScheduledLesson($timeslot : timeslot, $student : lesson.student)
        ScheduledLesson(timeslot == $timeslot + 1, lesson.student == $student)
    then
        scoreHolder.addHardConstraintMatch(kcontext, -1);
end

注意第4行中的timeslot == $timeslot + 1件。这给出了以下错误：

Exception in thread "main" java.lang.RuntimeException: Error evaluating constraint 'timeslot == $timeslot + 1' in [Rule "Student does not have contiguous lessons" filename]

这似乎与Drools documentation which touches on maths不符。我要去哪里错了，如何在Drools中实施此规则？

ScheduledLesson看起来像这样：

@PlanningEntity
public class ScheduledLesson {
    public Lesson lesson;

    public Lesson getLesson() {
        return this.lesson;
    }

    public void setLesson(Lesson lesson) {
        this.lesson = lesson;
    }

    public Integer timeslot;

    @PlanningVariable(valueRangeProviderRefs = {"timeslot"})
    public Integer getTimeslot() {
        return this.timeslot;
    }
    public void setTimeslot(Integer timeslot) {
        this.timeslot = timeslot;
    }

    public Room room;
    @PlanningVariable(valueRangeProviderRefs = {"room"})
    public Room getRoom() {
        return this.room;
    }
    public void setRoom(Room room) {
        this.room = room;
    }
}

谢谢。

Answer 1

在Java中，添加一个ScheduledLesson.getTimeslotIndex()return timeslot.getIndex()