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所以我试图弄清楚 MySQL 的关系，我编写了代码，但它似乎没有工作，好像我在我的数据库中添加了一些东西，每次另一个表的外键都给我 NULL，我的人际关系代码是：

用户等级：

    @OneToMany(mappedBy="user")
private Collection<Movie> movies;

    public Collection<Movie> getMovies() {
    return movies;
}
public void setMovies(Collection<Movies> movies) {
    this.movies = movies;
}

电影类：

@ManyToOne
    private User user;

    public User getUser() {
    return user;
}
public void setUser(User user) {
    this.user = user;
}

每次我添加新电影（假设与用户表连接）时，外键（user_id）在电影表中给我 null。总结一下我在这里要实现的目标，每次我想将电影添加到我的库中时，我都希望将拥有该电影的人的用户 ID 显示在数据库中。

谢谢。

编辑：

每次尝试运行它时，我都会收到此错误消息：

Exception in thread "main" javax.persistence.PersistenceException: org.hibernate.PropertyValueException: not-null property references a null or transient value: entity.Movie.user
at org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:614)
at org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:226)
at persistence.PersistenceUtil.persist(PersistenceUtil.java:26)
at main.CustomerConfig.main(CustomerConfig.java:47)

Caused by: org.hibernate.PropertyValueException: not-null property references a null or transient value: entity.Movie.user
    at org.hibernate.engine.Nullability.checkNullability(Nullability.java:95)
    at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:313)
    at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:204)
    at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:130)
    at org.hibernate.ejb.event.EJB3PersistEventListener.saveWithGeneratedId(EJB3PersistEventListener.java:49)
    at org.hibernate.event.def.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:154)
    at org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:110)
    at org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:61)
    at org.hibernate.impl.SessionImpl.firePersist(SessionImpl.java:645)
    at org.hibernate.impl.SessionImpl.persist(SessionImpl.java:619)
    at org.hibernate.impl.SessionImpl.persist(SessionImpl.java:623)
    at org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:220)

创建数据并将数据保存到数据库的代码：

System.out.println("Type the users's name please. ");
        String name = br.readLine();

        System.out.println("Type the movies name please. ");
        String mname = br.readLine();

        User user = new User(name);
        PersistenceUtil.persist(user);
        Movie movie = new Movie(mname);
        PersistenceUtil.persist(movie);
        System.out.println("User & movie names are created!");
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1 回答 1

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Movie movie = new Movie(mname);
PersistenceUtil.persist(movie);

正如错误所说，此对象的用户为空movie，您忘记在其中设置用户。这就是它的样子：

Movie movie = new Movie(mname);
movie.setUser(user);
PersistenceUtil.persist(movie);
于 2013-11-04T05:32:05.960 回答