[英]lazy loading entities in spring with jpa and hibernate
我在JPA和Hibernate中使用Spring。 我有一些用@Repositoy注释的DAO类和一些控制器类。 当我在控制器中调用dao的方法之一以加载某些实体时,我取回了Entity,然后,我想获取一些存储在第一个加载的实体的字段中的其他实体。 但是那时spring已经关闭了会话,并且不再可能进行延迟加载。
我的db.xml配置:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd
http://www.springframework.org/schema/data/jpa
http://www.springframework.org/schema/data/jpa/spring-jpa.xsd" default-autowire="byName">
<!-- Scans within the base package of the application for @Components to configure as beans -->
<bean id="placeholderConfig"
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="location" value="classpath:db.properties" />
</bean>
<tx:annotation-driven transaction-manager="transactionManager"/>
<!-- <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="jpaVendorAdapter" />
</bean> -->
<bean id="entityManagerFactory"
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="jpaVendorAdapter">
<bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
<property name="showSql" value="true" />
<property name="generateDdl" value="true" />
<property name="databasePlatform" value="${db.dialect}" />
</bean>
</property>
</bean>
<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
destroy-method="close">
<property name="driverClassName" value="${db.driver}" />
<property name="url" value="${db.url}" />
<property name="username" value="${db.username}" />
<property name="password" value="${db.password}" />
</bean>
<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager" />
</beans>
道中的方法注释如下:
@Transactional(readOnly = true, propagation=Propagation.REQUIRED)
现在我想做这样的事情:
@Controller
public class HomeController{
@Autowired
private UserDao userDao;
@RequestMapping(value = "/", method = RequestMethod.GET)
public ResponseEntity<String> home(){
...
User user = userDao.findUser(id);
Set<Order> orders = user.getOrders();
...
String myResult = ...;
return jsonService.generateResponse(myResult);
}
}
@Repository
public class UserDao{
@PersistenceContext
private EntityManager entityManager;
public User findUser(Integer id){
return entityManager.find(User.class, id);
}
}
订单集应延迟加载,但出现以下异常:org.springframework.web.util.NestedServletException:请求处理失败; 嵌套的异常是org.hibernate.LazyInitializationException:无法延迟初始化角色的集合:...,没有会话或会话被关闭
根本原因:org.hibernate.LazyInitializationException:无法延迟初始化角色集合:...,没有会话或会话被关闭
我试图对Controller wirt @Transactional中的方法进行注释,并且还在db.xml中的注释驱动属性中设置mode =“ aspectj”,但没有任何效果。 有什么办法可以延迟加载用户的订单?
对于任何帮助,感谢您的期待!
您可以使用特殊过滤器在Web视图中获取会话。 添加到您的web.xml
<filter>
<filter-name>jpaFilter</filter-name>
<filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>jpaFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
过滤器的工作原理如下:
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