Spring 4 + Hibernate 4 事务管理错误

Spring 4 + Hibernate 4 transaction management error

我对 Spring 的事务管理有点陌生。我想我缺少一些配置,但我无法处理它。

错误是我收到 failed to lazily initialize a collection of role 异常。

我正在为我的 DAO 使用 Spring 数据。另外,我知道将 fetchType 设置为 Eager,但这是我要避免的。

DAO:

public interface CourseDao extends CrudRepository<CourseEntity, Long> {
    CourseEntity findByName(String name);
}

服务:

@Service
public class CourseMaterialSearchService {
    private final CourseDao courseDao;
    private final CourseMaterialEntityTransformer courseMaterialEntityTransformer;

    @Autowired
    public CourseMaterialSearchService(CourseDao courseDao, CourseMaterialEntityTransformer courseMaterialEntityTransformer) {
        super();
        this.courseDao = courseDao;
        this.courseMaterialEntityTransformer = courseMaterialEntityTransformer;
    }

    @Transactional
    public List<CourseMaterial> findMaterialsFor(final Long courseId) {
        final CourseEntity entity = courseDao.findOne(courseId);
        final List<CourseMaterialEntity> materials = entity.getCourseMaterialEntityList();
        return courseMaterialEntityTransformer.transformEntities(materials);
    }
}

而我的申请-context.xml是(当然这只是相关部分):

<bean id="entityManagerFactory"
    class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="persistenceUnitName" value="example" />
    <property name="dataSource" ref="exampleDataSource" />
    <property name="packagesToScan" value="com.example.example.**.repository" />
    <property name="jpaVendorAdapter">
        <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
            <property name="showSql" value="true" />
            <property name="generateDdl" value="true" />
        </bean>
    </property>
</bean>
<tx:annotation-driven proxy-target-class="true" transaction-manager="transactionManager"/>

<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="entityManagerFactory" />
</bean>

当我调用CourseMaterialSearchService中的findMaterialsFor方法时,出现了异常。我该如何解决?

如有任何建议,我们将不胜感激。

谢谢大家。

堆栈跟踪:

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.example.example.course.repository.domain.CourseEntity.courseMaterialEntityList, could not initialize proxy - no Session
org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:575)
org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:214)
org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:554)
org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:142)
org.hibernate.collection.internal.PersistentBag.iterator(PersistentBag.java:294)
com.example.example.course.service.transform.CourseMaterialEntityTransformer.transformEntities(CourseMaterialEntityTransformer.java:15)
com.example.example.course.service.CourseMaterialSearchService.findMaterialsFor(CourseMaterialSearchService.java:29)

CourseMaterialEntityTransformer:

public class CourseMaterialEntityTransformer {
        public List<CourseMaterial> transformEntities(final Iterable<CourseMaterialEntity> entities) {
            final List<CourseMaterial> result = new ArrayList<>();
            for (final CourseMaterialEntity entity : entities) {
                result.add(transformEntity(entity));
            }
            return result;
        }

    public CourseMaterial transformEntity(final CourseMaterialEntity entity) {
        final CourseMaterial result = new CourseMaterial();
        result.setId(entity.getId());
        result.setName(entity.getName());
        result.setCourseName(entity.getCourseEntity().getName());
        result.setCurrentFileName(entity.getCurrentFileName());
        result.setOriginalFileName(entity.getOriginalFileName());
        result.setCategory(entity.getMaterialCategoryEntity().getName());
        result.setUploader(entity.getUserEntity().getName());
        return result;
    }
}

com.example.example.course.service.transform.CourseMaterialEntityTransformer.transformEntities(CourseMaterialEntityTransformer.java:15):

for (final CourseMaterialEntity entity : entities) {

课程实体:

@Entity(name = "courses")
public class CourseEntity {
    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @OneToMany(mappedBy = "courseEntity")
    private List<CourseMaterialEntity> courseMaterialEntityList;

    public Long getId() {
        return id;
    }

    public void setId(final Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(final String name) {
        this.name = name;
    }

    public List<CourseMaterialEntity> getCourseMaterialEntityList() {
        return courseMaterialEntityList;
    }

    public void setCourseMaterialEntityList(final List<CourseMaterialEntity> courseMaterialEntityList) {
        this.courseMaterialEntityList = courseMaterialEntityList;
    }

}

您正在尝试访问事务外的惰性加载属性。然后该对象与 EntityManager(数据库)没有任何联系,因为它在事务之外,因此无法获取延迟加载的属性。

默认情况下,集合是延迟加载的。您可以替换下面的代码:

@OneToMany(mappedBy = "courseEntity")
private List<CourseMaterialEntity> courseMaterialEntityList;

与:

@OneToMany(fetch = FetchType.EAGER, mappedBy = "courseEntity", cascade = CascadeType.ALL)
private List<CourseMaterialEntity> courseMaterialEntityList;

您需要将 @OneToMany(mappedBy = "courseEntity") 更改为 @OneToMany(mappedBy = "courseEntity", fetch = FetchType.EAGER, cascade = CascadeType.ALL)

默认的获取类型是惰性的,因此当您尝试访问该集合时,它尚未从数据库中加载。

Spring 使用 AOP 应用事务。 beans 上的 AOP 仅适用于同一应用程序上下文中的 beans。

您的 application-context.xml 中有一个 <tx:annotation-driven />,由 ContextLoaderListener 加载。此文件包含一个 <context:component-scan />,它检测 @Service.

但是,如果您在 DispatcherServlet 加载的文件中也有相同的 <context:component-scan />,或者至少如果检测到相同的 @Service,则会导致此服务的另一个实例不会应用 AOP。

作为一般的经验法则,您希望在 ContextLoaderListener 中加载除 @Controllers 之外的所有内容,并且只在 [=] 中加载与 Web 相关的内容(查看解析器,@Controllers) 16=]。

参见 context depended scan-component filter