关于Hibernate的延迟加载

Question

 

 为什么多对一的关系在hbm.xml文件中必须把class标签的lazy属性值必须设置成false才可以，还有返回查询返回List对象结果集时必须将hbm.xml文件的hibernate-mapping的属性default-lazy值设置成false否则就会出现下面的错误啊

 

 

08:42:43,546 ERROR LazyInitializationException:19 - could not initialize proxy - the owning Session was closed
org.hibernate.LazyInitializationException: could not initialize proxy - the owning Session was closed
at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:60)
at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:111)
at org.hibernate.proxy.pojo.cglib.CGLIBLazyInitializer.invoke(CGLIBLazyInitializer.java:172)

Answer 1

恩,是的.那个整合了spring.如果没整合spring的话你可以自己写一个过滤器,用来决定什么时候才关闭session.

还有,用了lazy=false会降低hibernate的数据检索效率.推荐使用fetch="join",然后在HQL语句中使用left join fetch的方式进行加载关联表的数据.