Java 为什么我在首先合并实体时将删除的实例传递给合并
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Why am I getting deleted instance passed to merge, when merging the entity first
提问by Rika
I believe the entity that I wish to delete, is a managed entity. But, regardless, why is merging it then removing it giving me the following error:
我相信我想删除的实体是一个托管实体。但是，无论如何，为什么合并它然后删除它会给我以下错误：
deleted instance passed to merge
删除的实例传递给合并
Someone said on stackoverflow that merge should be ignored if it is a managed entity. So why is this not being ignored?
有人在 stackoverflow 上说如果是托管实体，应该忽略合并。那么为什么这不被忽视呢？
The way I wish to delete it is like so:
我想删除它的方式是这样的：
TrialUser mergedEntity = em.merge(tu);
em.remove(mergedEntity);
But this errors, but if I get rid of the first line it seems to work fine. But I want it the other way because that is consistent with the rest of the code.
但是这个错误，但如果我去掉第一行，它似乎工作正常。但我想要另一种方式，因为这与代码的其余部分一致。
EDIT:
编辑：
@PersistenceContext(unitName = "UnitName")
protected EntityManager entityManager;
@Table(name="TRIAL_USER")
@Id
private BigDecimal id;
@ManyToOne(cascade= {CascadeType.ALL }, fetch=FetchType.EAGER)
@JoinColumn(name="TRIAL_USER_CLASS_ID3")
private TrialUserElement trialUserElement3;
@ManyToOne(cascade= {CascadeType.ALL }, fetch=FetchType.EAGER)
@JoinColumn(name="TRIAL_USER_CLASS_ID1")
private TrialUserElement trialUserElement1;
@ManyToOne(cascade= {CascadeType.ALL }, fetch=FetchType.EAGER)
@JoinColumn(name="TRIAL_USER_CLASS_ID2")
private TrialUserElement trialUserElement2;
回答by Dick Chesterwood
This is bit of a shot in the dark as I can't run your code, and these types of problems can turn out to be a bit complex. But rest assured that it should be fine to merge and then delete. I suspect it may be related to your many to one associated entities.
由于我无法运行您的代码，因此这有点像在黑暗中进行，而这些类型的问题可能会变得有点复杂。不过放心，合并再删除应该没问题。我怀疑它可能与您的多对一关联实体有关。
At the point where the transaction commits, the remove is being cascaded to the linked entities.
在事务提交的时候，remove 被级联到链接的实体。
Even though the merge is redundant for your parent entity, I think the merge is being cascaded to the child entities, which have been deleted, hence the exception.
即使合并对于您的父实体来说是多余的，但我认为合并正在级联到已删除的子实体，因此是例外。
Try changing your cascade rules - pull it back to CascadeType.MERGE (for all three) and see if you still get the exception. Or change to CascadeType.DELETE, this will prevent the necessary merge being cascaded.
尝试更改您的级联规则 - 将其拉回 CascadeType.MERGE（对于所有三个），看看您是否仍然遇到异常。或者更改为 CascadeType.DELETE，这将阻止必要的合并被级联。
回答by uaiHebert
The JPA SPEC says that:
JPA SPEC 说：
3.2.7.1 Merging Detached Entity State
If X is a removed entity instance, an IllegalArgumentException will be thrown by the merge operation (or the transaction commit will fail).
3.2.7.1 合并分离的实体状态
如果 X 是已删除的实体实例，则合并操作将抛出 IllegalArgumentException（否则事务提交将失败）。
That is why you cannot merge a deleted entity.
这就是您不能合并已删除实体的原因。
回答by Spyna
You can have this error when you run some code into a transaction, when you commit at the end og the method. When using spring in a method or class annotated with
当您在事务中运行一些代码时，当您在最后提交该方法时，您可能会遇到此错误。在带有注释的方法或类中使用 spring 时
@Transactional
This happens because you first delete the object (without committing) and then try to update it.
发生这种情况是因为您首先删除了对象（不提交），然后尝试更新它。
this code will generate the exception:
此代码将生成异常：
@Transactional
myethod(){
dao.delete(myObject);
myObject.setProperty("some value");
dao.save();
}
To avoid the error you should not delete and then save in the same transaction.
为避免该错误，您不应删除并保存在同一事务中。
