org.hibernate.id.IdentifierGenerationException：尝试从空的一对一属性（使用session.merge）分配ID

Question

I have a problem. I get error in my app: org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property

My pojos User:

@Entity
@Table(name = "user")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class User implements Serializable {
private static final long serialVersionUID = -5415891222321582213L;

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "userId", length = 100)
private int userId;
...
@OneToOne(mappedBy = "user", cascade = CascadeType.ALL)
private UserDetail userDetail;

UserDetail:

@Entity
@Table(name = "userdetail")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class UserDetail implements Serializable {
private static final long serialVersionUID = 2155190440305692224L;

@Id
@GenericGenerator(
    name = "gen",
    strategy = "foreign",
    parameters = @Parameter(name = "property", value = "user")
    )
@GeneratedValue(generator = "gen")
@Column(name = "userId", length = 100)
private int userId;
...
@OneToOne
@PrimaryKeyJoinColumn
private User user;

Table User:

CREATE TABLE `user` (
    `userId` INT(100) NOT NULL AUTO_INCREMENT,
    `name` VARCHAR(255) NULL DEFAULT NULL,
    `surname` VARCHAR(255) NULL DEFAULT NULL,
    `email` VARCHAR(255) NULL DEFAULT NULL,
    `password` VARCHAR(255) NULL DEFAULT NULL,
    PRIMARY KEY (`userId`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
;

Table UserDetail

CREATE TABLE `userdetail` (
    `userId` INT(100) NOT NULL,
    `country` VARCHAR(255) NULL DEFAULT NULL,
    `city` VARCHAR(255) NULL DEFAULT NULL,
    `address` VARCHAR(255) NULL DEFAULT NULL,
    PRIMARY KEY (`userId`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
;

DAO Layer:

private Session session = HibernateUtil.getHibernateUtil().getSession();
@Override
public void create(T t) throws DaoException {
        Object object = session.merge(t);
        session.save(object);
        log.info("Update: " + t);
}

Service Layer

private Session session = HibernateUtil.getHibernateUtil().getSession();
private Transaction transaction = null;
private Dao<T> dao = new BaseDao<T>();
@Override
public void create(T t) throws DaoException {
    try {
        transaction = session.beginTransaction();
        dao.create(t);
        transaction.commit();
        log.info("Create: " + t);
    } catch (HibernateException e) {
        log.error("Error creating " + getPersistentClass() + " in Dao " + e);
        transaction.rollback();
        throw new DaoException(e);
    }
}

Class with saving User

User user = new User(name, surname, email, password);
UserDetail userDetail = new UserDetail(country, city, address);
user.setUserDetail(userDetail);
userDetail.setUser(user);
userService.create(user);

HiberUtil

public class HibernateUtil {
    private static Logger log = Logger.getLogger(HibernateUtil.class);
    private static HibernateUtil util = null;
    private static SessionFactory sessionFactory = null;
    private static final ThreadLocal<Session> sessions = new ThreadLocal<Session>();

    private HibernateUtil() {
        try {
        Configuration configuration = new Configuration().configure("hibernate.cfg.xml");
        log.info("Hibernate Configuration loaded");
        ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
        log.info("Hibernate serviceRegistry created");
        sessionFactory = configuration.buildSessionFactory(serviceRegistry);
        } catch (Throwable e) {
            log.error("Initial SessionFactory creation failed. " + e);
            System.exit(0);
        }
    }

    public Session getSession () {
        Session session = sessions.get();
        if (session == null) {
            session = sessionFactory.openSession();
            sessions.set(session);
        } 
        return session;
    }

    public static synchronized HibernateUtil getHibernateUtil(){
        if (util == null){
            util = new HibernateUtil();
        }
        return util;
    }
}

If i change in DAO layer:

@Override
public void create(T t) throws DaoException {
        session.save(t);
        log.info("Create: " + t);
}

I get error: org.hibernate.HibernateException: Illegal attempt to associate a collection with two open sessions

So I have 4 questions:

1. If I understood correctly, when userdeteil save userId from User is null because UserId don't get icnrement Id from Table, it's true?

2. Needed session.merge here or not

3. If merge is needed, how correct org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property

4. If merge is no needed, how correct "org.hibernate.HibernateException: Illegal attempt to associate a collection with two open sessions"

Note: Delet with merge is good, create with merge other Entity (not User and not UserDeteil) is good.

Answer 1

To get it work, remove Object object = session.merge(t); from update method of your DAO class. Here is updated update method

@Override
public void update(T t) throws DaoException {
        session.saveOrUpdate(t);
        log.info("Update: " + t);
}

This will fix your org.hibernate.id.IdentifierGenerationException exception.

• For point 1: Your record was not saved, you were calling merge() method, then the object return by merge method is passed in save(here). merger(): Copy the state of the given object onto the persistent object with the same identifier. In your case no persistent object.
• For point 2: No merge method is not required here, use save or saveOrUpdate method with session
• For point 3: N/A

Here is a good example of One-To-One association mapping

Answer 2

I solved my poroblem. In my BaseDao and BaseService I removed:

private Session session = HibernateUtil.getHibernateUtil().getSession();

And I added in all methods in BaseDao and BaseService:

HibernateUtil.getHibernateUtil().getSession();

so I removed the two sessions and my method, example create, became:

@Override
public void create(T t) throws DaoException {
        HibernateUtil.getHibernateUtil().getSession().save(t);
        log.info("Create: " + t);
}