java - Hibernate一对多关系: can't remove children once parent is removed

Question

我有类(class)评论一对多关系。在类(class)表中有 id 和 title 列。在 Review 表中，有 id、comment 和 course_id，其中“course_id”作为指向类(class) id 的 FK。我想实现这样的场景:一旦类(class)被删除，相关的评论应该自动删除。我有以下代码:

@Entity
@Table(name = "course")
public class Course {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;

    @Column(name = "title")
    private String title;

    @OneToMany(mappedBy = "course", fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true)
    private List<Review> reviews;

    public void addReview(Review review){
        if(reviews==null) reviews = new ArrayList<>();
        reviews.add(review);
    }

    //other codes below omitted
}



@Entity
@Table(name = "review")
public class Review {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;

    @Column(name = "comment")
    private String comment;

    @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(name = "course_id")
    private Course course;

//other codes omitted
}

客户端代码:

public class Client_OneToMany_bidirectional {
    public static void main(String[] args) {

        SessionFactory sf = new Configuration()
                .configure("hibernate.cfg.xml")
                .addAnnotatedClass(Instructor.class)
                .addAnnotatedClass(InstructorDetail.class)
                .addAnnotatedClass(Course.class)
                .addAnnotatedClass(Review.class)
                .buildSessionFactory();

        Session session = sf.getCurrentSession();

        try{
            //add course and review
            Course course = new Course("How to learn Java");

            course.addReview(new Review("Good course!"));
            course.addReview(new Review("I love it!"));
            course.addReview(new Review("Need some more!"));

            session.beginTransaction();
            System.out.println(course);
            System.out.println(course.getReviews());
            session.save(course);
            session.getTransaction().commit();

            //start to delete the course
            session = sf.getCurrentSession();
            session.beginTransaction();
            Course crs = session.get(Course.class, 12);
            if(crs != null ){
                session.delete(crs);
            }
            session.getTransaction().commit();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            session.close();
            sf.close();
        }
    }
}

我发现我可以成功删除类(class)，但三个评论没有被删除。在搜索 stackoverflow 相关帖子后我也尝试使用 orphanRemoval=true 但它仍然不起作用。

Answer 1

您的评论从未真正属于该类(class)，因为您从未初始化该协会的所有权部分:Review.course。将您的 addReview() 方法更改为

@OneToMany(mappedBy = "course", fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true)
private List<Review> reviews = new ArrayList<>();

public void addReview(Review review){
    review.setCourse(this);
    reviews.add(review);
}