org.hibernate.LazyInitializationException：懒惰初始化角色集合失败（Hibernate + Spring）

Question

我有一个带有以下文件的 SpringMVC+Hibernate Web 应用程序：

applicationContext.xml

    <bean id="dataSource" destroy-method="close" class="org.apache.commons.dbcp.BasicDataSource">
    <property name="driverClassName" value="org.postgresql.Driver"/>
    <property name="url" value="jdbc:postgresql://localhost:5432/db"/>
    <property name="username" value="kjhkjkj"/>
    <property name="password" value="dsfa@efe45"/>
</bean>

<bean id="txManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
    <property name="sessionFactory" ref="hibernateSessionFactory"/>
</bean>

<bean id="transactionProxy" class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean">
    <property name="transactionManager" ref="txManager"/>
    <property name="transactionAttributes">
        <props>
            <prop key="*">PROPAGATION_REQUIRED</prop>
        </props>
    </property>
    <property name="target">
        <bean class="dao.DocumentViewDao">
            <property name="sessionFactory" ref="hibernateSessionFactory"/>
        </bean>
    </property>
    <property name="proxyTargetClass" value="true"/>
</bean>

<bean id="hibernateSessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
    <property name="dataSource" ref="dataSource"/>
    <property name="mappingResources">
        <list>
    <value>orm/Document.hbm.xml</value>
    <value>orm/UploadedDocument.hbm.xml</value>
    <!-- More resource files go here -->
        </list>
    </property>
    <property name="hibernateProperties">
        <value>
            hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect
            hibernate.show_sql = true
            hibernate.format_sql = true
            hibernate.generate_statistics = true
            hibernate.cache.use_query_cache = true
            hibernate.cache.use_second_level_cache = true
            hibernate.cache.provider_class = org.hibernate.cache.EhCacheProvider
            hibernate.query.substitutions = true 't', false 'f'
        </value>
    </property>
</bean>

<bean id="documentViewDao" class="dao.DocumentViewDao">
    <property name="sessionFactory" ref="hibernateSessionFactory"/>
</bean>

dao.DocumentViewDao

@Transactional
public class DocumentViewDao extends HibernateDaoSupport
{
public List all ( )
        throws HibernateException
{
    Session session = this.getSessionFactory ( ).getCurrentSession ( );

    return session.createQuery ( new StringBuilder ( 35 )
                    .append ( "SELECT d.id AS id, d.identifier AS identifier, d.title AS title, u.version AS version, u.effectFrom AS effectFrom " )
                    .append ( "FROM Document AS d " )
                    .append ( "LEFT OUTER JOIN d.uploadedDocumentsById AS u " )
                    .append ( "WITH u.isCurrent = true" )
                    .toString ( ) )
            .setCacheable ( true )
            .setResultTransformer( Transformers.ALIAS_TO_ENTITY_MAP )
            .list ( );
}

public Document getDocument ( int documentId )
        throws HibernateException
{
    Session session = this.getSessionFactory ( ).getCurrentSession ( );

    Document document = null;

    Query q = session.createQuery ( "FROM IsoDocument AS d " +
                                    "LEFT OUTER JOIN FETCH d.uploadedDocumentsById " +
                                    "WHERE d.id = :documentId"
    );
    q.setParameter ( "documentId", documentId );
    q.setCacheable ( true );
    document = ( Document ) q.uniqueResult ( );

    return document;
}
}

controller.DocumentController

public class DocumentController implements Controller
{   
    public ModelAndView handleRequest ( HttpServletRequest request, HttpServletResponse response )
            throws Exception
    {
        ModelAndView modelAndView = new ModelAndView ( "document" );

        WebApplicationContext context = ContextLoader.getCurrentWebApplicationContext ( );
        DocumentViewDao documentViewDao = ( DocumentViewDao ) context.getBean ( "transactionProxy" );

        Document document = DocumentViewDao.getDocument ( Integer.parseInt ( request.getParameter ( "id" ) ) );
        modelAndView.addObject ( "document", document );

        return modelAndView;
    }
}

ORM 类和映射应该没问题，我不会写（丢了行 :)） 所以问题是我得到了

org.hibernate.LazyInitializationException: 延迟初始化角色集合失败：orm.Document.uploadedDocumentsById，没有会话或会话关闭

controller.DocumentController 生成的页面刷新时。显然，缓存和事务存在我无法解决的问题。此外，使用 dao.DocumentViewDao 中的 all() 不会抛出这样的异常（但查询中没有 FETCH）。那么你有什么想法吗？我也很乐意收到有关此代码的任何 cmets 和/或建议以改进它（我是 Spring 和 Hibernate 的新手）。

Answer 1

当返回实体实例的查询是可缓存的并且您有缓存命中时，缓存仅返回实体的 ID，然后使用会话加载实体.这意味着当您有缓存命中时，不再应用连接 fecth。这也意味着查询返回的所有实体实例也应该在二级缓存中，否则性能实际上可能比没有查询缓存时更差。

因此，您应该在 DAO 中使用 Hibernate.initialize(document.getUploadedDocumentsById() 以确保它已被初始化。