java - OneToMany 子实体在 save() 上未持久化

Question

我在 hibernate 中遇到了以下行为，我无法解释，我希望有人能够解释正在发生的事情。

我在 Instructor 和 Course 之间建立了双向 @OneToMany 关联。由于他们有一个 CascadeType.PERSIST ，我希望当我创建一个 Course 对象并将其关联到 Instructor 时，反之亦然，然后调用讲师的 .save() 方法这两个对象都将保留在数据库中，尽管这会导致仅保留 Instructor 而无需保留类(class)。

如果我调用 persist() 方法，例如:session.persist(instructor)，讲师和类(class)都会被保留。

这是我的实体和主要方法。

导师:

@Entity
@Table(name = "instructor")
public class Instructor {

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

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;

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

    @OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    @JoinColumn(name = "instructor_detail_id")
    private InstructorDetail instructorDetail;

    @OneToMany(mappedBy = "instructor", cascade = {CascadeType.DETACH,
    CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH}, fetch = FetchType.LAZY)
    private List<Course> courses = new ArrayList<>();

    public Instructor() {
    }

    public Instructor(String firstName, String lastName, String email) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public InstructorDetail getInstructorDetail() {
        return instructorDetail;
    }

    public void setInstructorDetail(InstructorDetail instructorDetail) {
        this.instructorDetail = instructorDetail;
    }

    public List<Course> getCourses() {
        return courses;
    }

    public void setCourses(List<Course> courses) {
        this.courses = courses;
    }

    @Override
    public String toString() {
        return "Instructor{" +
            "id=" + id +
            ", firstName='" + firstName + '\'' +
            ", lastName='" + lastName + '\'' +
            ", email='" + email + '\'' +
            ", instructorDetail=" + instructorDetail +
            ", courses=" + courses +
            '}';
    }

    public void addCourse(Course course) {
        courses.add(course);
        course.setInstructor(this);
    }
}

类(class)

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

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

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

    @ManyToOne(cascade = {CascadeType.DETACH, CascadeType.MERGE,
        CascadeType.PERSIST, CascadeType.REFRESH}, fetch = FetchType.LAZY)
    @JoinColumn(name = "instructor_id")
    private Instructor instructor;

    public Course(String title) {
        this.title = title;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public Instructor getInstructor() {
        return instructor;
    }

    public void setInstructor(Instructor instructor) {
        this.instructor = instructor;
    }
}

主要

public class Test {

    public static void main(String[] args) {

        //create session factory
        SessionFactory sessionFactory = new Configuration()
            .configure("com/ysoft/config/hibernate.cfg.xml")
            .addAnnotatedClass(Instructor.class)
            .addAnnotatedClass(InstructorDetail.class)
            .addAnnotatedClass(Course.class)
            .buildSessionFactory();

        //create session
        Session session = sessionFactory.getCurrentSession();

        try (sessionFactory) {
            session.beginTransaction();

            Instructor instructor = new Instructor("John", "Doe", "John.Doe@email.com");
            InstructorDetail instructorDetail = new InstructorDetail("http://www.something.com", "Coding");

            Course mathCourse = new Course("Math");
            Course englishCourse = new Course("English");
            Course sportsCourse = new Course("Sports");

            instructor.addCourse(mathCourse);
            instructor.addCourse(englishCourse);
            instructor.addCourse(sportsCourse);

            instructor.setInstructorDetail(instructorDetail);

            session.save(instructor);

            session.getTransaction().commit();

            System.out.println("Persisted" + instructor);
        }
    }
}

Answer 1

如果我将 @OneToMany 级联数组更改为 CascadeType.ALL 那么它就可以工作 - 但我不知道为什么，因为相关类型已经存在。

子端不应指定级联 - 引用最新的 Hibernate 文档:

The @OneToMany association is by definition a parent association, even if it’s a unidirectional or a bidirectional one. Only the parent side of an association makes sense to cascade its entity state transitions to children.

更新:

根据this似乎调用 save() 而不是使用 JPA EntityManager.persist() 它还需要 Hibernate 特定的级联类型 SAVE_UPDATE。 (这与 JPA @OneToMany 定义不兼容)