小编Tit*_*tus的帖子

我得到了一个典型的订单和物品的实体关联。为了使只读订单成为可能，项目设置为默认FetchType.LAZY。2级和查询缓存已启用。要读取具有关联项目的订单，我正在使用JPQL查询。查询和实体由EHCache缓存。但是在访问项目时的第二次调用中，引发了LazyInitializationException异常，因为未初始化项目（未从缓存还原）。为什么？实施此要求的最佳方法是什么？

订购：

@Entity
@Cacheable
@NamedQueries({
  @NamedQuery(name = Order.NQ_FIND_BY_ID_FETCH_ITEMS, query = "SELECT DISTINCT o FROM Order o JOIN FETCH o.items WHERE o.id = :id")
})
@Table(...)
public class Order extends ... {
  ...
  @OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
  // @Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
  private Set<Item> items = new HashSet<Item>();
  ...
}

项目：

@Entity
@Cacheable
@Table(...)
public class Item extends ... {
  @ManyToOne
  @JoinColumn(name = "order_id", nullable = false)
  private Order order;
  ...
}

道：

public class OrderDaoJpaImpl extends …

我在Tomcat 7中运行的Web应用程序中使用Spring 3.2和JPA以及Hibernate 4.应用程序分为控制器,服务DAO类.服务类在类和方法级别具有带注释的事务配置.DAO是普通的JPA,实体管理器由@PersistenceContext注释注入.

@Service("galleryService")
@Transactional(propagation=Propagation.SUPPORTS, readOnly=true)
public class GalleryServiceImpl implements GalleryService {

  @Override
  public Picture getPicture(Long pictureId) {
    return pictureDao.find(pictureId);
  }

  @Override
  public List<PictureComment> getComments(Picture picture) {
    List<PictureComment> comments = commentDao.findVisibleByPicture(picture);
    Collections.sort(comments, new Comment.ByCreatedOnComparator(Comment.ByCreatedOnComparator.SORT_DESCENDING));
    return comments;
  }
  ...
}

@Controller
@RequestMapping("/gallery/displayPicture.html")
public class DisplayPictureController extends AbstractGalleryController {

  @RequestMapping(method = RequestMethod.GET)
  public String doGet(ModelMap model, @RequestParam(REQUEST_PARAM_PICTURE_ID) Long pictureId) {
    Picture picture = galleryService.getPicture(pictureId);
    if (picture != null) {
      model.addAttribute("picture", picture);
      // Add comments
      model.addAttribute("comments", galleryService.getComments(picture));
    } else {
      LOGGER.warn(MessageFormat.format("Picture {0} …