关于merge与IdTransferringMergeEventListener的用法

newObj = getHibernateTemplate().merge(obj);

obj是一个游离对象，该方法将把obj中的属性更新到与obj主键一致的持久对象中，并返回该持久对象newObj。如果没有对应的持久对象，将会新建一个持久对象并将属性拷贝进去，并返回新对象。

参考：

Copy the state of the given object onto the persistent object with the same identifier. Follows JSR-220 semantics.

Similar to saveOrUpdate , but never associates the given object with the current Hibernate Session. In case of a new entity, the state will be copied over as well.

Note that merge will not update the identifiers in the passed-in object graph (in contrast to TopLink)! Consider registering Spring's IdTransferringMergeEventListener if you would like to have newly assigned ids transferred to the original object graph too.

 

如果上述方法新建了一个持久对象，持久对象的id并不会拷贝到obj中。如果想要拷贝到obj中，要注册IdTransferringMergeEventListener 监听器。

例如：

xml 代码

		<property name="eventListeners">
			<map>
				<entry key="merge">
					<bean
						class="org.springframework.orm.hibernate3.support.IdTransferringMergeEventListener" />
				</entry>
			</map>
		</property>