保存我的实体时，我得到了一个非常奇怪的 NullPointerException，我似乎无法弄清楚为什么。
java.lang.NullPointerException: null
at org.hibernate.type.AbstractType.getHashCode(AbstractType.java:129)
at java.base/java.util.stream.Collectors.lambda$groupingBy$53(Collectors.java:1127)
at java.base/java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1654)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)
at org.hibernate.collection.internal.PersistentBag.groupByEqualityHash(PersistentBag.java:196)
at org.hibernate.collection.internal.PersistentBag.equalsSnapshot(PersistentBag.java:151)
at org.hibernate.engine.spi.CollectionEntry.dirty(CollectionEntry.java:158)
at org.hibernate.engine.spi.CollectionEntry.preFlush(CollectionEntry.java:182)
at org.hibernate.event.internal.AbstractFlushingEventListener.lambda$prepareCollectionFlushes$0(AbstractFlushingEventListener.java:195)
at org.hibernate.engine.internal.StatefulPersistenceContext.forEachCollectionEntry(StatefulPersistenceContext.java:1091)
at org.hibernate.event.internal.AbstractFlushingEventListener.prepareCollectionFlushes(AbstractFlushingEventListener.java:194)
at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:86)
at org.hibernate.event.internal.DefaultAutoFlushEventListener.onAutoFlush(DefaultAutoFlushEventListener.java:50)
at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:108)
at org.hibernate.internal.SessionImpl.autoFlushIfRequired(SessionImpl.java:1323)
at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1403)
at org.hibernate.query.internal.AbstractProducedQuery.doList(AbstractProducedQuery.java:1558)
at org.hibernate.query.internal.AbstractProducedQuery.list(AbstractProducedQuery.java:1526)
at org.hibernate.query.Query.getResultList(Query.java:165)
[...] the rest was cut for readability (if you think it's really important, I'll edit and add the whole exception, but I think it's the first line that says it all)
这是由于上述原因而引发的更高异常：
org.springframework.transaction.TransactionSystemException: Could not commit JPA transaction; nested exception is javax.persistence.RollbackException: Error while committing the transaction
at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:542)
这个嵌套的：
Caused by: javax.persistence.RollbackException: Error while committing the transaction
at org.hibernate.internal.ExceptionConverterImpl.convertCommitException
我整天都在兜圈子，试图弄清楚为什么会发生这种情况，而互联网没有帮助，因为大多数类似的问题仍未得到解答。更糟糕的是 Spring 的抽象使得它无法调试！
这是场景：我有一个EventEntity我正在尝试更新的，以及它的子实体EventAttachmentEntity。我已打开日志记录以跟踪正在发生的事情，并且几乎预期会发生：
- 我已经更新了 eventEntity（更新 SQL 生成）
- 我为更新的事件插入了新附件（插入使用正确 event_id 生成的 SQL）
然后奇怪的事情发生了，我的方法走到了尽头，然后发生了这个异常。
由于公开原因，该方法被抽象出来，但主要流程如下：
@Transactional(rollbackFor = Exception.class)
public void updateEvent(EventEntity event) {
EventEntity updatedEvent = eventRepository.save(event);
EventAttachmentEntity newAttachment = new EventAttachmentEntity(updatedEvent);
// fill attachment [...]
newAttachment.setEvent(updatedEvent);
eventAttachmentRepository.save(newAttachment);
System.out.println("This line gets printed.");
}
所以首先我保存更新的父级，然后创建新的子级，设置父级，然后保存它。所有 SQL 都确认这是发生的情况。最后一行也会打印出来，这意味着以前的保存方法没有任何问题。然后它到了尽头，砰！例外。
这是我的实体：
@Entity
@Table(name = "event", schema = "xxx")
@DynamicUpdate
public class EventEntity {
private long id;
private Collection<EventAttachmentEntity> eventAttachments;
// other properties abstracted
@OneToMany(mappedBy = "event")
public Collection<EventAttachmentEntity> getEventAttachments() {
return this.eventAttachments;
}
public void setEventAttachments(Collection<EventAttachmentEntity> eventAttachments) {
this.eventAttachments = eventAttachments;
}
}
@Entity
@Table(name = "event_attachment", schema = "xxx")
public class EventAttachmentEntity {
private long id;
private String filename;
private String contentType;
private long filesize;
private EventEntity event;
// other properties abstracted
@ManyToOne
@JoinColumn(name = "event_id", referencedColumnName = "id", nullable = false)
public EventEntity getEvent() {
return event;
}
public void setEvent(EventEntity event) {
this.event = event;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
EventAttachmentEntity that = (EventAttachmentEntity) o;
return id == that.id &&
filesize == that.filesize &&
Objects.equals(filename, that.filename) &&
Objects.equals(contentType, that.contentType);
}
@Override
public int hashCode() {
return Objects.hash(id, filename, contentType, filesize);
}
}
我已经包含了 EventAttachmentEntity 的equals()和hashCode()方法，因为异常显然发生在getHashCode()，但是当我将断点放在那里时，它实际上是调用 getHashCode 的 Object 为空。
重要说明：我检查了我的代码中的任何变量是否为空或没有正确自动装配 - 一切都很好。就像我说的那样，该方法本身运行平稳，直到它到达最后并尝试提交事务。那是它破裂的时候。
此外，当我尝试仅更新事件（不带附件）时，一切正常。我尝试过的另一种情况是保存此事件的类似关系（此处未显示），它也可以正常工作。所以它与附件有关，我无法弄清楚它是什么！
同样奇怪的是，如果我@Transactional从这个方法中删除，它会抛出同样的异常。没有@Transactional标记的方法正在调用updateEvent()，所以我不确定这是怎么发生的。
拜托，我需要任何关于可能是什么问题的建议，所以我可以尝试一下，因为现在我几乎碰壁了，无法继续。