使用Hibernate實作JPA，關於PersistentObjectException: detached entity passed to persist的解決方法

主要使用元件：

• Oracle TopLink Essentials v1 Build 48


• Hibernate Core v3.2.6.ga


• Hibernate Annotations v3.3.1.GA


• Hibernate Entity Manager v3.3.2.GA


• Spring Framework v2.5.5 LocalContainerEntityManagerFactoryBean

User和Address為bidirectional one-to-many的關係，在User有以下的property acccessor：

@OneToMany(cascade={CascadeType.REFRESH, CascadeType.REMOVE}, fetch=FetchType.EAGER, mappedBy="user")
public Set<Address> getAddresses() {
    return Addresses;
}

在Address有以下的property acccessor：

@ManyToOne(cascade={CascadeType.ALL}, optional=false)
@JoinTable(name="address_user")
public User getUser() {
    return this.user;
}

先persist User之後，persist Address時會丟出以下的Exception：

javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist: User
    at org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:637)
    at org.hibernate.ejb.AbstractEntityManagerImpl.persist (AbstractEntityManagerImpl.java:226)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.springframework.orm.jpa.ExtendedEntityManagerCreator$ExtendedEntityManagerInvocationHandler.invoke(ExtendedEntityManagerCreator.java:358)
    at $Proxy24.persist(Unknown Source)
...

原因：這是由於「CascadeType.ALL」包含「CascadeType.PERSIST」，導致persist Address時傳播了這個動作到User，使得persisted User重複地被persist。

解決方法：修改Address的@ManyToOne annotation，移除cascade={CascadeType.ALL}。只要cascade不包含CascadeType.PERSIST就不會丟出Exception，例如

@ManyToOne(cascade={CascadeType.MERGE, CascadeType.REFRESH, CascadeType.REMOVE}, optional=false)