Hibernate正常，但ElipseLink失败：类[Y]的属性[x]映射到数据库中的主键列不允许更新

Question

我有一个非常简单的基于控制台的（不是应用服务器部署的）JPA程序，我对Eclipse Link和Hibernate提供商进行了测试。所有的代码都是JPA，所以我想我可以毫无问题地切换提供商。然而，当使用Hibernate作为提供程序时，程序会成功，但在Eclipse Link中会失败。

关键部分是这个（我在防火墙后面，所以我看不到格式，因为“所以需要来自另一个域的JavaScript…”因此，如果格式不正确，我深表歉意-我将在家中进行格式设置）：

em.getTransaction().begin();
Employee emp = service.createEmployee(id, "John Doe", 45000,1);
em.getTransaction().commit();                                        
System.out.println("Persisted "+emp);
em.getTransaction().begin();
em.getTransaction().commit();

我曾经在第二个空事务中做过一些事情，但在缩小问题范围时，我注意到即使我不做任何事情就立即开始（）和提交（），它也会失败。有趣的是EclipseLink（见文章底部的stack trace）似乎抱怨entity Speciality的id属性正在更新，尽管它没有更新。

员工实体具有专业实体的外键（每个员工都有一个专业），即员工的多对一关系：

 @Entity
 public class Employee {
 @Id                                                            
 @Basic(optional = false)                                       
 @NotNull                                                       
 private int id;                                                
 private String name;                                           
 private long salary;                                           
 @JoinColumn(name = "spc_id", referencedColumnName = "id")      
 @ManyToOne(optional = false)                                   
 private Specialty spcId;
 ...}

专业类定义为：

@Entity                                                  
public class Specialty {                                 
@Id                                                  
@Basic(optional = false)                             
@NotNull                                             
private int id;
... }

当使用Hibernate作为JPA提供程序时，代码执行平稳。当使用EclipseLink时，它会失败，因为在本文底部找到了堆栈跟踪。

更新：经过进一步的实验，我发现以下代码适用于两个提供商：

em.getTransaction().begin();                                      
Employee emp = service.createEmployee(id, "John Doe", 45000, 1);  
em.getTransaction().commit();                                     
System.out.println("Persisted " + emp);                           
EntityManager em2 = emf.createEntityManager();
em2.getTransaction().begin();                                     
em2.getTransaction().commit();                                    
em2.close();          

这仍然不能解释为什么EclipseLink在尝试在同一个实体管理器对象上开始（）/commit（）事务时失败（em-请参阅本文开头的代码），而且还不能解释为什么它会因为这样一条神秘的消息而失败（抱怨类Speciality的主键正在更新）。

堆栈跟踪：

[java] [EL Info]: 2012-07-12 11:21:09.453--ServerSession(23846608)--EclipseLink, version: Eclipse Persistence Services - 2.4.0.v20120608-r11652
 [java] [EL Info]: connection: 2012-07-12 11:21:09.59--ServerSession(23846608)--file:/home/mperdikeas/playground/jpa/01-employee-job/prj/use/build/employeetest.jar_EmployeeService login successful
 [java] Exception in thread "main" javax.persistence.RollbackException: Exception [EclipseLink-7251] (Eclipse Persistence Services - 2.4.0.v20120608-r11652): org.eclipse.persistence.exceptions.ValidationException
 [java] Exception Description: The attribute [id] of class [mp.Specialty] is mapped to a primary key column in the database. Updates are not allowed.
 [java]     at org.eclipse.persistence.internal.Persisted mp.Employee@ea70f2
 [java] [EL Warning]: 2012-07-12 11:21:09.735--UnitOfWork(32118258)--Exception [EclipseLink-7251] (Eclipse Persistence Services - 2.4.0.v20120608-r11652): org.eclipse.persistence.exceptions.ValidationException
 [java] Exception Description: The attribute [id] of class [mp.Specialty] is mapped to a primary key column in the database. Updates are not allowed.
 [java] [EL Info]: connection: 2012-07-12 11:21:09.738--ServerSession(23846608)--file:/home/mperdikeas/playground/jpa/01-employee-job/prj/use/buildjpa.transaction.EntityTransactionImpl.commitInternal(EntityTransactionImpl.java:102)
 [java]     at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commit(EntityTransactionImpl.java:63)
 [java]     at mp.EmployeeTest.main(EmployeeTest.java:29)
 [java] Caused by: Exception [EclipseLink-7251] (Eclipse Persistence Services - 2.4.0.v20120608-r11652): org.eclipse.persistence.exceptions.ValidationException
 [java] Exception Description: The attribute [id] of class [mp.Specialty] is mapped to a primary key column in the database. Updates are not allowed.
 [java]     at org.eclipse.persistence.exceptions.ValidationException.primaryKeyUpdateDisallowed(ValidationException.java:2458)
 [java]     at org.eclipse.persistence.mappings.foundation.AbstractDirectMapping.writeFromObjectIntoRowWithChangeRecord(AbstractDirectMapping.java:1214)
 [java]     at org.eclipse.persistence.internal.descriptors.ObjectBuilder.buildRowForUpdateWithChangeSet(ObjectBuilder.java:1378)
 [java]     at org.eclipse.persistence.internal.queries.DatabaseQueryMechanism.updateObjectForWriteWithChangeSet(DatabaseQueryMechanism.java:1003)
 [java]     at org.eclipse.persistence.queries.UpdateObjectQuery.executeCommitWithChangeSet(UpdateObjectQuery.java:84)
 [java]     at org.eclipse.persistence.internal.queries.DatabaseQueryMechanism.executeWriteWithChangeSet(DatabaseQueryMechanism.java:286)
 [java]     at org.eclipse.persistence.queries.WriteObjectQuery.executeDatabaseQuery(WriteObjectQuery.java:58)
 [java]     at org.eclipse.persistence.queries.DatabaseQuery.execute(DatabaseQuery.java:852)
 [java]     at org.eclipse.persistence.queries.DatabaseQuery.executeInUnitOfWork(DatabaseQuery.java:751)
 [java]     at org.eclipse.persistence.queries.ObjectLevelModifyQuery.executeInUnitOfWorkObjectLevelModifyQuery(ObjectLevelModifyQuery.java:108)
 [java]     at org.eclipse.persistence.queries.ObjectLevelModifyQuery.executeInUnitOfWork(ObjectLevelModifyQuery.java:85)
 [java]     at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.internalExecuteQuery(UnitOfWorkImpl.java:2875)
 [java]     at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1602)
 [java]     at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1584)
 [java]     at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1535)
 [java]     at org.eclipse.persistence.internal.sessions.CommitManager.commitChangedObjectsForClassWithChangeSet(CommitManager.java:265)
 [java]     at org.eclipse.persistence.internal.sessions.CommitManager.commitAllObjectsWithChangeSet(CommitManager.java:128)
 [java]     at org.eclipse.persistence.internal.sessions.AbstractSession.writeAllObjectsWithChangeSet(AbstractSession.java:3914)
 [java]     at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.commitToDatabase(UnitOfWorkImpl.java:1419)
 [java]     at org.eclipse.persistence.internal.sessions.RepeatableWriteUnitOfWork.commitToDatabase(RepeatableWriteUnitOfWork.java:634)
 [java]     at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.commitToDatabaseWithChangeSet(UnitOfWorkImpl.java:1509)
 [java]     at org.eclipse.persistence.internal.sessions.RepeatableWriteUnitOfWork.commitRootUnitOfWork(RepeatableWriteUnitOfWork.java:266)
 [java]     at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.commitAndResume(UnitOfWorkImpl.java:1147)
 [java]     at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commitInternal(EntityTransactionImpl.java:84)
 [java]     ... 2 more
 [java] /employeetest.jar_EmployeeService logout successful

Answer 1

尝试

Answer 2

它可能是：

@Entity                                                  
public class Specialty {                                 
@Id                                                  
@Basic(optional = false)                             
@NotNull
@GeneratedValue(strategy = GenerationType.AUTO)                                         
private int id;
... }

Answer 3

Eclipse Link不允许您更新PK（如果这个PK没有任何FK，一些DBMS允许这样做）

周围有2个工作：

1. 尝试删除旧记录，然后插入新记录