System.out.println("id:"+category.getId()+" ,name:"+category.getName()+", description:"+category.getDescription()); 输出的是id,name和description属性值,其他的我们不管,所以Hibernate用了lazy loading(延迟加载),带来的好处就是我们不关心的 数据,不用现在加载,当我们要用的时候,才去加载 测试代码二: ...
通过class的lazy属性,可以打开实体对象的延迟加载功能。(映射文件) (Hibernate2中,lazy默认为false;Hibernate3默认true) 非延迟加载的例子: <hibernate-mapping><classname="...TUser"table="t_user"dynamic-update="false"dynamic-insert="false"select-before-update="false"optimistic-lock="version"lazy="false">...
Lazy Loading(懒加载)是一种延迟加载策略,即只有在真正需要对象的数据时才从数据库中加载。Hibernate通过代理模式来实现懒加载,当访问一个实体的属性时,Hibernate会检查该属性是否已经被加载,如果没有,则执行相应的SQL语句从数据库中获取数据。 二、Hibernate Lazy Loading的实现原理 Hibernate使用动态代理来实现懒加载。...
1,针对实体对象的延迟加载: 在class标签里添加lazy="true",属性: <class name="TUser" table="t_user" lazy="true"> 如果将lazy="false"时,当程序运行: TUser user = (TUser) session.load(TUser.class, new Integer(1)); 时,会发出SQL,从数据库中取出所对应的记录,并构造了一个完整的TUser对象;...
Hibernate中的懒加载(Lazy Loading)可能会导致空指针异常。当一个对象的属性被标记为懒加载,Hibernate会在真正需要访问该属性时才从数据库中加载它。如果在访问这个属性之前,对象没有被正确初始化或者已经被关闭的Session中,那么就会抛出空指针异常。 解决方法: ...
Session per request is a transactional pattern to tie the persistence session and request life-cycles together. Not surprisingly, Spring comes with its own implementation of this pattern, named OpenSessionInViewInterceptor, to facilitate working with lazy associations and therefore, improving developer pr...
org.hibernate.LazyInitializationException: illegal access to loading collection 异常是 Hibernate 在处理延迟加载(Lazy Loading)集合属性时抛出的一个异常。它表明在 Hibernate 会话(Session)关闭后,尝试访问了一个延迟加载的集合属性,这是不允许的。 2. 可能导致该异常的场景和原因 会话关闭后的访问:在 Hibernate 会...
The wrong way is to useFetchType.EAGER. Instead of fixing the problem, it replaces it with another inefficiency. This would only be a good idea, if every time you fetch anOrderentity, you also need the associatedOrderItems. But that’s usually not the case. ...
I modeled a one-to-one association and activated lazy loading for it. But it doesn’t work. How do I tell Hibernate to fetch a one-to-one association lazily? Solution: Configuring lazy loading for one-to-one associations is not as easy as it is forother associations. For all other ass...
we did not specify a proper unsaved-value strategy for the entity two users tried to delete the same row at almost the same time we manually set a value in the autogenerated ID or version field 7. Lazy Initialization Errors We usually configure associations to be loaded lazily to improve ap...