Question

我有：

@Entity
public class EmailAndName {
...
}

和

@Entity
public class MessageDetails {
    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinTable(name = "MessageDetails_to")
    public Set<EmailAndName> getTo() {
        return to;
    }
}

当我

public static void main(String []a)
{
    StatelessSession sess = HibernateUtils.getSessionFactory().openStatelessSession();
    sess.beginTransaction();
    MessageDetails messageDetails = new MessageDetails();
    messageDetails.setTo(new HashSet<EmailAndName>());
    EmailAndName emailAndName = (EmailAndName) sess.get(EmailAndName.class, 1L);
    if (emailAndName == null ) throw new RuntimeException();
    messageDetails.getTo().add(emailAndName);
    sess.insert(messageDetails);
    sess.getTransaction().commit();
}

未填充MessageDetails_to表。我该怎么办？我不想写本机查询。谢谢。

Answer 1

您尚未通读hibernate-doc无状态会话

它明确指出：

Operations performed using a stateless session never cascade to associated instances. Collections are ignored by a stateless session.

您正在尝试添加Set<EmailAndName>。无状态会话是较低级别的抽象，更接近底层JDBC。所以如果你真的想让你的代码工作并填充MessageDetails_to ..你需要去Session。您需要为POJO定义equals和hashCode方法:)

所以修改后的代码将是：

public static void main(String []a)
{
   try{
    Session sess = HibernateUtils.getSessionFactory().openSession();
    sess.beginTransaction();
    MessageDetails messageDetails = new MessageDetails();
    messageDetails.setTo(new HashSet<EmailAndName>());
    EmailAndName emailAndName = (EmailAndName) sess.get(EmailAndName.class, 1L);
    if (emailAndName == null ) throw new RuntimeException();
    messageDetails.getTo().add(emailAndName);
    sess.save(messageDetails);
    sess.getTransaction().commit();
 }
catch(HibernateException e)
 {
   sess.getTransaction.rollback();
   e.printStackTrace();
 }
  finally{
       sess.close();
  }

你必须总是附上一个try catch，这样你就可以识别异常（如果有的话）并使它工作:)

Answer 2

首先，您确定交易是否已提交？

其次，您使用的是Set。您确定equals类的hashCode和EmailAndName方法定义明确吗？

Answer 3

好吧，我认为你的代码不工作的主要原因是由于使用无状态会话，但无论如何我会建议你在实现1-N和NM关系时定义反向的关系并更新双方。

另外，不要让外部类直接操作集合，因为它打破了封装。不要为集合公开set方法，这可能会导致非常难以调试的异常异常。使用添加和删除方法来更新您的设置。

@Entity
public class MessageDetails {

    private Set<EmailAndName> to = new HashSet<EmailAndName>();

    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinTable(name = "MessageDetails_to", 
       joinColumns = {@JoinColumn(name = "MESSAGE_DETAILS_ID"},
       inverseJoinColumns = {@JoinColumn(name = "EMAIL_AND_ADDRESS_ID")})
    public Set<EmailAndName> getTo() {
        return Collections.unmodifiableSet(to);
    }

    public void addEmaiAndName(EmailAndName emailAndName) {
       emailAndName.setMessageDetails(this);
       to.add(emailAndName);
    }

    public void removeEmailAndName(EmailAndName emailAndName) {
       emailAndName.setMessageDetails(null);
       to.remove(emailAndName);
    }

}

代码的另一部分应该是：

Session sess = HibernateUtils.getSessionFactory().openSession();
sess.beginTransaction();
MessageDetails messageDetails = new MessageDetails();
EmailAndName emailAndName = (EmailAndName) sess.get(EmailAndName.class, 1L);
if (emailAndName == null ) throw new RuntimeException();
messageDetails.addEmailAndName(emailAndName);
sess.save(messageDetails);
sess.getTransaction().commit();

使用无状态会话保存ManyToMany集合

3 个答案: