Drools collect list from object property

问题

I have a student, who have list of courses. Also I have a lectures and I need to check that student courses list and list of courses of lectures that he visits are same

I added rule for case, when student visits lecture, that he doesn't have in courses list:

    when
        $student:Student ($courses:courses) 
        LectureAssignment(student == $student, course not memberOf $courses)
    then
        scoreHolder.addHardConstraintMatch(kcontext, -1);

But I also need to check, that student visits all lecture, that he have in courses list

    $student:Student ($courses:courses)
    $rightCourses: collect (LectureAssignment(student == $student)) // and get courses list

here I get lectures, that assigned to current student , all lectures have property course and I need to collect them into list $rightCourses and after this compare $courses and $rightCourses (in this case I think I don't need first rule)

回答1:

You could use forall operator. See documentation here [1]. If that doesn't work for you, you could use accumulate [2], checking that the lecture count a student has assigned is correct, with a combination of your first rule that checks that a student has not assigned a course that is not part of the courses list.

[1] https://docs.jboss.org/drools/release/7.16.0.Final/drools-docs/html_single/index.html#_conditional_element_forall
[2] https://docs.jboss.org/drools/release/7.16.0.Final/drools-docs/html_single/index.html#_conditional_element_accumulate

来源：https://stackoverflow.com/questions/54182500/drools-collect-list-from-object-property