@IdClass使用JPA和Hibernate生成“实例的标识符已更改" [英] @IdClass Produces 'Identifier of an Instance was Altered' with JPA and Hibernate
问题描述
对于使用不区分大小写的数据库架构的JPA实体模型，当我使用@IdClass批注时，我始终会收到实例标识符已更改"异常.对于具有字符串"主键的对象，如果数据库中存在一种情况的字符串，并且仅使用大小写不同的同一字符串执行查询，就会发生错误.
For a JPA entity model using a case-insensitive database schema, when I use a @IdClass annotation I consistently get 'identifier of an instance was altered' exception. For an object with a 'string' primary key, the error occurs when an string of one case exists in the database and a query is performed with the same string differing only in case.
我看过其他的SO答案，它们的形式是:a)不要修改主键(我不是)，b)你的equals()/hashCode()实现有缺陷.对于'b'，我尝试使用toLowerCase()和equalsIgnoringCase()，但无济于事. [另外，Hibernate代码似乎是直接设置属性，而不是在发生更改"时调用属性设置器.]
I've looked at other SO answers and they are of the form: a) don't modify the primary key (I'm not) and b) your equals()/hashCode() implementations are flawed. For 'b' I've tried using toLowerCase() and equalsIgnoringCase() but to no avail. [Additionally, it seems the Hibernate code is directly setting properties, rather than calling property setters when the 'altering' occurs.]
这是具体错误:
Caused by: javax.persistence.PersistenceException: org.hibernate.HibernateException:
identifier of an instance of db.Company was altered
from {Company.Identity [62109154] ACURA}
to {Company.Identity [63094242] Acura}
问:对于包含公司"Acura"(作为主键)的不区分大小写的数据库，如何使用@IdClass随后查找其他大写字母?
这是有问题的代码(从一个空的数据库开始):
Here is the offending code (starting with an empty database):
public class Main {
public static void main(String[] args) {
EntityManagerFactory emf =
Persistence.createEntityManagerFactory("mobile.mysql");
EntityManager em = emf.createEntityManager();
em.getTransaction().begin();
Company c1 = new Company ("Acura");
em.persist(c1);
em.getTransaction().commit();
em.getTransaction().begin();
c1 = em.find (Company.class, new Company.Identity("ACURA"));
em.getTransaction().commit();
em.close();
System.exit (0);
}
}
这是"db.Company"实现:
and here is the 'db.Company' implementation:
@Entity
@IdClass(Company.Identity.class)
public class Company implements Serializable {
@Id
protected String name;
public Company(String name) {
this.name = name;
}
public Company() { }
@Override
public int hashCode () {
return name.hashCode();
}
@Override
public boolean equals (Object that) {
return this == that ||
(that instanceof Company &&
this.name.equals(((Company) that).name));}
@Override
public String toString () {
return "{Company@" + hashCode() + " " + name + "}";
}
//
public static class Identity implements Serializable {
protected String name;
public Identity(String name) {
this.name = name;
}
public Identity() { }
@Override
public int hashCode () {
return name.hashCode();
}
@Override
public boolean equals (Object that) {
return this == that ||
(that instanceof Identity &&
this.name.equals(((Identity)that).name));
}
@Override
public String toString () {
return "{Company.Identity [" + hashCode() + "] " + name + "}";
}
}
}
注意:我知道只有一个主键时就不需要使用@IdClass了；上面是问题的最简单的例子.
Note: I know using @IdClass isn't needed when there is a single primary key; the above is the simplest example of the problem.
正如我所说，我相信即使将hashCode()/equals()方法不区分大小写，这个问题仍然存在.但是，还是采取了建议.
As I said, I believe this problem persists even when the hashCode()/equals() methods are made case insensitive; however, suggestions taken.
...
INFO: HHH000232: Schema update complete
Hibernate: insert into Company (name) values (?)
Hibernate: select company0_.name as name1_0_0_ from Company company0_ where company0_.name=?
Exception in thread "main" javax.persistence.RollbackException: Error while committing the transaction
at org.hibernate.jpa.internal.TransactionImpl.commit(TransactionImpl.java:94)
at com.lambdaspace.Main.main(Main.java:24)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
Caused by: javax.persistence.PersistenceException: org.hibernate.HibernateException: identifier of an instance of db.Company was altered from {Company.Identity [62109154] ACURA} to {Company.Identity [63094242] Acura}
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1763)
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1677)
at org.hibernate.jpa.internal.TransactionImpl.commit(TransactionImpl.java:82)
... 6 more
Caused by: org.hibernate.HibernateException: identifier of an instance of db.Company was altered from {Company.Identity [62109154] ACURA} to {Company.Identity [63094242] Acura}
at org.hibernate.event.internal.DefaultFlushEntityEventListener.checkId(DefaultFlushEntityEventListener.java:80)
at org.hibernate.event.internal.DefaultFlushEntityEventListener.getValues(DefaultFlushEntityEventListener.java:192)
at org.hibernate.event.internal.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:152)
at org.hibernate.event.internal.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:231)
at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:102)
at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:55)
at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1222)
at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:425)
at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101)
at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:177)
at org.hibernate.jpa.internal.TransactionImpl.commit(TransactionImpl.java:77)
... 6 more
推荐答案
发生此错误的原因是由于更改了受管实体的实体标识符.
The reason for this error is due to changing the entity identifier of a managed entity.
在PersistenceContext的生存期内，任何给定实体只能有一个且只有一个托管实例.为此，您不能更改现有的受管实体标识符.
During the life-time of a PersistenceContext, there can be one and only one managed instance of any given entity. For this, you can't change an existing managed entity identifier.
在您的示例中，即使您开始新事务，也必须记住PersistenContext尚未关闭，因此您仍将一个托管的c1实体附加到Hibernate会话.
In you example, even if you start a new transaction, you must remember that the PersistenContext has not been closed, so you still have a managed c1 entity attached to the Hibernate Session.
当您尝试查找公司时:
c1 = em.find (Company.class, new Company.Identity("ACURA"));
该标识符与当前会话所附公司的标识符不匹配，因此发出查询:
The identifier doesn't match the one for the Company that's being attached to the current Session, so a query is issued:
Hibernate: select company0_.name as name1_0_0_ from Company company0_ where company0_.name=?
由于SQL是CASE INSENSITIVE，因此您实际上将选择与当前托管的Company实体(持久化的c1)相同的数据库行.
Because SQL is CASE INSENSITIVE, you will practically select the same database row as the current managed Company entity (the persisted c1).
但是对于同一数据库行，您只能有一个受管实体，因此Hibernate将重用该受管实体实例，但会将标识符更新为:
But you can have only one managed entity for the same database row, so Hibernate will reuse the managed entity instance, but it will update the identifier to:
new Company.Identity("ACURA");
您可以通过以下测试检查这一假设:
You can check this assumptions with the following test:
String oldId = c1.name;
Company c2 = em.find (Company.class, new Company.Identity("ACURA"));
assertSame(c1, c2);
assertFalse(oldId.equals(c2.name));
在提交第二笔交易时，刷新将尝试更新实体标识符(已从"Acura"更改为"ACURA")，因此
When the second transaction is committed, the flush will try to update the entity identifier (which changed from 'Acura' to 'ACURA') and so the DefaultFlushEntityEventListener.checkId() method will fail.
根据JavaDoc，此检查适用于:
According to teh JavaDoc, this check is for:
确保用户没有篡改ID
make(ing) sure (the) user didn't mangle the id
要修复此问题，您需要删除以下查找方法调用:
To fix it, you need to remove this find method call:
c1 = em.find (Company.class, new Company.Identity("ACURA"));
您可以检查是否已连接c1:
You can check that c1 is already attached:
assertTrue(em.contains(c1));
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