Hibernate 延迟加载的错误
2010-02-28 10:32
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关键字: failed to lazily initialize a collection of role
转自:http://www.qingsoft.net/bbs/html/article/1175.jhtml
用户和角色
用户User中有Set<Role> roles = new HashSet<Role>(0);
当得到User中的roles集合时,会出现下面的异常:
Java代码
Java代码
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.demo.security.entity.User.roles, no session or session was closed
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.demo.security.entity.User.roles, no session or session was closed
1. 当时我的解决是:
UserDAOImpl.java
Java代码
Java代码
@SuppressWarnings("unchecked")
public List<User> queryAll(final Integer isInitialize) {
return getHibernateTemplate().executeFind(new HibernateCallback(){
public Object doInHibernate(Session session)
throws HibernateException, SQLException {
Query q = session.createQuery("from User u left join fetch u.userInfo");
if(isInitialize == 0) return q.list();
else{
List<User> users = q.list();
for(User user : users){
if(isInitialize ==1)
getHibernateTemplate().initialize(user.getRoles());
}
return users;
}
return q.list();
}});
}
@SuppressWarnings("unchecked") public List<User> queryAll(final Integer isInitialize) { return getHibernateTemplate().executeFind(new HibernateCallback(){ public Object doInHibernate(Session session) throws HibernateException, SQLException { Query q = session.createQuery("from User u left join fetch u.userInfo"); if(isInitialize == 0) return q.list(); else{ List<User> users = q.list(); for(User user : users){ if(isInitialize ==1) getHibernateTemplate().initialize(user.getRoles()); } return users; } return q.list(); }}); }
感觉这样写比较麻烦,觉得效率上也不高。
2. 看到网上有的是把lazy=false,在Hibernate Annotation中也这样的(注意红色部分)
Java代码
Java代码
@ManyToMany(
targetEntity = Role.class,
cascade = {CascadeType.PERSIST, CascadeType.MERGE},
fetch = FetchType.EAGER)
@JoinTable(
name = "User_Role",
joinColumns = {@JoinColumn(name = "User_Id")},
inverseJoinColumns = {@JoinColumn(name = "Role_Id")})
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public Set<Role> getRoles() {
return roles;
}
@ManyToMany( targetEntity = Role.class, cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.EAGER) @JoinTable( name = "User_Role", joinColumns = {@JoinColumn(name = "User_Id")}, inverseJoinColumns = {@JoinColumn(name = "Role_Id")}) @Cache(usage = CacheConcurrencyStrategy.READ_WRITE) public Set<Role> getRoles() { return roles; }
要是这样,效率更是糟糕(不管要不要某个数据,都会查询出来,很是浪费)
最后看了篇文章:
就是使用filter,过滤所有的链接
如果在使用filter的时候,要配置事务处理,否则会导致session处于只读状态而不能做修改、删除的动作
web.xml
XML/HTML代码
Xml代码
<filter>
<filter-name>hibernateFilter</filter-name>
<filter-class>
org.springframework.orm.hibernate3.support.OpenSessionInViewFilter
</filter-class>
</filter>
<filter-mapping>
<filter-name>hibernateFilter</filter-name>
<url-pattern>*.action</url-pattern>
</filter-mapping>
<filter> <filter-name>hibernateFilter</filter-name> <filter-class> org.springframework.orm.hibernate3.support.OpenSessionInViewFilter </filter-class> </filter> <filter-mapping> <filter-name>hibernateFilter</filter-name> <url-pattern>*.action</url-pattern> </filter-mapping>
上面的fetch = FetchType.EAGER 改成 fetch = FetchType.LAZY
是这样解释的:
Spring为我们解决最让人头痛的难题之一,Hibernate的Session的关闭与开启问题。
Hibernate 允许对关联对象、属性进行延迟加载,但是必须保证延迟加载的操作限于同一个 Hibernate Session 范围之内进行。如果 Service 层返回一个启用了延迟加载功能的领域对象给 Web 层,当 Web 层访问到那些需要延迟加载的数据时,由于加载领域对象的 Hibernate Session 已经关闭,这些导致延迟加载数据的访问异常。而Spring为我们提供的OpenSessionInViewFilter过滤器为我们很好的解决了这个问题。OpenSessionInViewFilter的主要功能是使每个请求过程绑定一个 Hibernate Session,即使最初的事务已经完成了,也可以在 Web 层进行延迟加载的操作。OpenSessionInViewFilter 过滤器将 Hibernate Session 绑定到请求线程中,它将自动被 Spring 的事务管理器探测到。所以 OpenSessionInViewFilter 适用于 Service 层使用HibernateTransactionManager 或 JtaTransactionManager 进行事务管理的环境,也可以用于非事务只读的数据操作中。
request-->open session-->打开连接、开始事务-->持久操作-->渲染(关闭连接、session)-->response
其中一些过程省略了,不是很关心。
不知道这是不是比较好的解决办法?等待各位老师和同学发表自己的看法。
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