对于使用不区分大小写的数据库模式的 JPA 实体模型,当我使用 @IdClass 注释时,我始终会收到“实例标识符已更改”异常。对于主键为'string'的对象,当数据库中存在一个大小写的字符串,并使用相同的字符串进行查询,仅大小写不同时,就会出现错误。
我看过其他 SO 答案,它们的形式是:a) 不要修改主键(我没有)和 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。 [此外,Hibernate 代码似乎是直接设置属性,而不是在发生“改变”时调用属性 setter 。]
具体错误如下:
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,使用 @IdClass 我随后如何查找其他大写字母?
这是有问题的代码(从一个空数据库开始):
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);
}
}
这里是“db.Company”的实现:
@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:我知道当只有一个主键时不需要使用@IdClass
;以上是该问题最简单的例子。
正如我所说,即使 hashCode()/equals() 方法不区分大小写,我相信这个问题仍然存在;但是,采纳了建议。
...
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
最佳答案
此错误的原因是由于更改了托管实体的实体标识符。
在 PersistenceContext 的生命周期内,任何给定实体只能有一个托管实例。为此,您不能更改现有的托管实体标识符。
在您的示例中,即使您启动了一个新事务,您也必须记住 PersistenContext 尚未关闭,因此您仍然有一个附加到 Hibernate session 的托管 c1
实体。
当您尝试寻找公司时:
c1 = em.find (Company.class, new Company.Identity("ACURA"));
标识符与附加到当前 session 的公司的标识符不匹配,因此发出查询:
Hibernate: select company0_.name as name1_0_0_ from Company company0_ where company0_.name=?
因为 SQL 是不区分大小写的,所以您实际上会选择与当前托管公司实体(持久化的 c1
)相同的数据库行。
但同一数据库行只能有一个托管实体,因此 Hibernate 将重用托管实体实例,但它会将标识符更新为:
new Company.Identity("ACURA");
您可以通过以下测试来检查此假设:
String oldId = c1.name;
Company c2 = em.find (Company.class, new Company.Identity("ACURA"));
assertSame(c1, c2);
assertFalse(oldId.equals(c2.name));
当提交第二个事务时,刷新将尝试更新实体标识符(从“Acura”更改为“ACURA”),因此 DefaultFlushEntityEventListener.checkId()方法将失败。
根据 JavaDoc,此检查用于:
make(ing) sure (the) user didn't mangle the id
要修复它,您需要删除此查找方法调用:
c1 = em.find (Company.class, new Company.Identity("ACURA"));
您可以检查 c1
是否已附加:
assertTrue(em.contains(c1));
关于java - @IdClass 使用 JPA 和 Hibernate 生成 'Identifier of an Instance was Altered',我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/28231818/