为什么我得到这个NullPointer异常？ [英] Why am I getting this NullPointer exception?

问题描述

两个表，一个主键是另一个的外键（Legacy DB）

我使用双向一对一映射：

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;
}

问题出在运行时：

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();

      }}

，它抛出此异常：

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

推荐答案

这篇文章： http：// forum。 hibernate.org/viewtopic.php?t=970823)

似乎表明注释3.2.x存在某种问题。你用的是什么版本？如果它是3.2.x，请尝试3.3或3.4。

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.

这篇关于为什么我得到这个NullPointer异常？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！