Why am I getting this NullPointer exception?

Question

Two tables, primary key of one is foreign key of another (Legacy DB)
I used bi-directional one to one mapping:

@Entity
public class First {
    @Id protected int a;

    @OneToOne(mappedBy ="first", cascade = CascadeType.PERSIST)
    @JoinColumn(name = "a")
    protected Second second;
}


@Entity
public class Second {

    @Id protected int a;

    @OneToOne
    @JoinColumn(name = "a", insertable = false)
    First first;
}

The problem is when running:

public class Persister {

    public static void main(String[] args) {

     EntityManagerFactory aEntityManagerFactory;
     EntityManager aEntityManager;  
     aEntityManagerFactory =
                       Persistence.createEntityManagerFactory("bibit_notification_jpa");
     aEntityManager = aEntityManagerFactory.createEntityManager();

     Second aSecond = new Second();
     aSecond.a = 1;   

     First aFirst = new First();
     aFirst.a = 1;
     aFirst.second = aSecond;

     aEntityManager.getTransaction().begin();
     aEntityManager.persist(aFirst);
     aEntityManager.getTransaction().commit();

      }}

, it throws this exception:

Exception in thread "main" javax.persistence.PersistenceException: java.lang.NullPointerException
    at org.hibernate.ejb.Ejb3Configuration.configure(Ejb3Configuration.java:252)
    at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:120)
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:51)
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:33)
    at Persister.main(Persister.java:14)
Caused by: java.lang.NullPointerException
    at org.hibernate.cfg.OneToOneSecondPass.doSecondPass(OneToOneSecondPass.java:135)
    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1130)
    at org.hibernate.cfg.AnnotationConfiguration.secondPassCompile(AnnotationConfiguration.java:296)
    at org.hibernate.cfg.Configuration.buildMappings(Configuration.java:1115)
    at org.hibernate.ejb.Ejb3Configuration.buildMappings(Ejb3Configuration.java:1233)
    at org.hibernate.ejb.EventListenerConfigurator.configure(EventListenerConfigurator.java:154)
    at org.hibernate.ejb.Ejb3Configuration.configure(Ejb3Configuration.java:869)
    at org.hibernate.ejb.Ejb3Configuration.configure(Ejb3Configuration.java:183)
    at org.hibernate.ejb.Ejb3Configuration.configure(Ejb3Configuration.java:240)
    ... 4 more

Answer 1

This post: http://forum.hibernate.org/viewtopic.php?t=970823)

Seems to indicate that there's some kind of problem with annotations 3.2.x. What version are you using? If it's 3.2.x, try 3.3 or 3.4.

Answer 2

You may want to have a look at the second example in the JavaDoc. If I read this correctly the code should be

@Entity
public class First {
    @Id protected int a;

    @OneToOne @PrimaryKeyJoinColumn
    protected Second second;
}

@Entity
public class Second {

    @Id protected int a;

    @OneToOne @PrimaryKeyJoinColumn
    First first;
}