我有以下JSON：

{
    id: 123,
    subObjects: [
        {
            id: 564,
            name: "foo",
            contry: {
                id: 1,
                name: "Germany"
            }
        },
        {
            id: 777,
            name: "bar",
            contry: {
                id: 1,
                name: "Germany"
            }
        }
    ]   
}

并使用Gson反序列化它。之后，我需要合并JPA实体：

Model model = new Gson().fromJson(json, modelClass);
model = entityManager.merge(model)

刷新从模型级联到子对象，再级联到各个国家。这会导致Hibernate出现异常“已将实体副本分配给其他实体”。

如果我使用其他国家/地区，则可以使用。如果我使用将国家/地区实例从一个对象复制到另一个对象，那么这两个子对象都引用该对象的同一实例，则该方法有效。

两国具有相同的价值观。两者也具有相同的hashCode。两国是平等的，但不是==，因为它们是不同的情况。

我正在使用Hibernate 4.1.3 Final和Gson 2.2

java.lang.IllegalStateException: An entity copy was already assigned to a different entity.
    at org.hibernate.event.internal.EventCache.put(EventCache.java:184)
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:285)
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:151)
    at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:914)
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:896)
    at org.hibernate.engine.spi.CascadingAction$6.cascade(CascadingAction.java:288)
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:380)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:323)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:165)
    at org.hibernate.event.internal.DefaultMergeEventListener.cascadeOnMerge(DefaultMergeEventListener.java:439)
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:308)
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:151)
    at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:914)
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:896)
    at org.hibernate.engine.spi.CascadingAction$6.cascade(CascadingAction.java:288)
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:380)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:323)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
    at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:409)
    at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:350)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:326)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:165)
    at org.hibernate.event.internal.DefaultMergeEventListener.cascadeOnMerge(DefaultMergeEventListener.java:439)
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:308)
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:151)
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:76)
    at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:904)
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:888)
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:892)
    at org.hibernate.ejb.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:874)
    at play.db.jpa.GenericModel.merge(GenericModel.java:234)
    [...]

我该如何以通用的方式解决此问题，而无需知道对象类型以及哪些对象在逻辑上是相同的？