Question

我已在cascades JPA和hibernate上阅读了几篇帖子。我尝试过所有这些，但都没有帮助。

我正在尝试保存一个Movie对象（与Actor有oneToMany关联）。电影对象是持久的，但与电影关联的演员对象不是。

这是我的entity课程：

@Entity
public class Movie {

    @Id
    @Column(name="MOVIE_ID")
    @GeneratedValue
    private Long id;

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

    @Column(name="Date_Released")
    private Date date;

    @OneToMany(mappedBy="movie",fetch=FetchType.EAGER,cascade=CascadeType.PERSIST)
    private Set<Actor> actors=new HashSet<>();

    public Movie(){}

    public Movie(String name, Date released){
        this.name=name;
        this.date=released;
    }


    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public Set<Actor> getActors() {
        return actors;
    }

    public void setActors(Set<Actor> actors) {
        this.actors = actors;
    }

    public String toString(){
        return  id + " : " + name + " : " + date;
    }

    public void addActor(Actor a){
        getActors().add(a);
    }

}

@Entity
public class Actor {
    @Id
    @Column(name="ACTOR_ID")
    @GeneratedValue
    private Long id;

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

@ManyToOne(fetch=FetchType.EAGER)
@JoinColumn(name="ACTOR_MOVIE")
private Movie movie;


public Actor(){}

public Actor(String name){
    this.name=name;
}


public Long getId() {
    return id;
}

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


public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}


public Movie getMovie() {
    return movie;
}

public void setMovie(Movie movie) {
    this.movie = movie;
}

public String toString(){
    return name + " : " + movie.getName();
}

}

场景1 将电影与演员

相关联

public class HibernateTest {

    public static void main(String[] args) {

           Movie movie1 = new Movie("Mr and Mrs.Smith", new Date(2005, 6, 5));
           Actor actor3=new Actor("Brad");
           Actor actor4=new Actor("Joe"); 
           movie1.getActors().add(actor3);
           movie1.getActors().add(actor4);

        SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
        Session session = sessionFactory.openSession();
        session.beginTransaction();
        session.persist(movie1);
        session.getTransaction().commit();
        session.close();

     }
}

当我查看表格时，我看到在电影表中创建了一行，在actor表中看到了两行。但没有关联。这是actor表上的actor_movie（foreign column）为空。

场景2 ：将Actor与电影相关联

我也试过这个：

public class HibernateTest {

        public static void main(String[] args) {

   Movie movie = new Movie("Titanic", new Date(1997,12,19));
        Actor actor1=new Actor("Leo");
        Actor actor2=new Actor("Kate");
        actor1.setMovie(movie);
        actor2.setMovie(movie); 

       SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
            Session session = sessionFactory.openSession();
            session.beginTransaction();
            session.persist(movie1);
            session.getTransaction().commit();
            session.close();
}
}

这里我注意到在数据库中，一行在影片表中保留，但在actor表中没有持久的行。

我不明白为什么这两种情况失败了？请说明为什么会出错？

非常感谢

Answer 1

由于Movie和Actor之间存在双向关联，因此必须相互设置。

情景1

public class HibernateTest {

    public static void main(String[] args) {

           Movie movie1 = new Movie("Mr and Mrs.Smith", new Date(2005, 6, 5));
           Actor actor3=new Actor("Brad");
           actor3.setMovie(movie1); // Missing in ur code
           Actor actor4=new Actor("Joe"); 
           actor4.setMovie(movie1); // Missing in ur code
           movie1.getActors().add(actor3);
           movie1.getActors().add(actor4);

        SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
        Session session = sessionFactory.openSession();
        session.beginTransaction();
        session.persist(movie1);
        session.getTransaction().commit();
        session.close();

     }
}

情景2

public class HibernateTest {

        public static void main(String[] args) {

   Movie movie = new Movie("Titanic", new Date(1997,12,19));
        Actor actor1=new Actor("Leo");
        Actor actor2=new Actor("Kate");
        actor1.setMovie(movie);
        actor2.setMovie(movie); 
        movie.getActors.add(actor1); // missing in ur code
        movie.getActors.add(actor2); // missing in ur code

       SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
            Session session = sessionFactory.openSession();
            session.beginTransaction();
            session.persist(movie1);
            session.getTransaction().commit();
            session.close();
}

}

希望这有帮助。

有关详情，请参阅我的博客Here

JPA Cascade在双向关联中不使用Hibernate？

1 个答案: