休眠一对多关系：一旦父母被移除就无法移除孩子

Question

我有一个课程评论一对多的关系。在课程表中有 id 和 title 列。在 Review 表中有 id、comment 和 course_id，其中“course_id”作为 FK 指向 Course id。我想实现这样的场景，一旦课程被删除，相关的评论就会被自动删除。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}

Answer 1

您的评论从未真正属于该课程，因为您从未初始化关联的拥有部分：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);

}