java - Java Spring 中的延迟加载异常

Question

在我的 Controller 中，我有以下代码获取数据库中的特定表示，将其添加为模型属性并返回详细 View :

@RequestMapping(value = "/detail", method = RequestMethod.GET)
public String detail(Model model, Principal principal, @RequestParam("id") int id) {
        Presentation p = presentationDao.get(id);
        model.addAttribute("presentation", p);
        return "detail";
}

在我看来，我正在尝试使用 JSTL 显示具有延迟加载功能的演示文稿的属性:

${pressentation.student.dossiers.proposal.titel}

但是在 Student 中有一个“文件”列表，但它使用延迟加载:

@OneToMany(mappedBy = "student", fetch = FetchType.LAZY)
private List<Dossier> dossiers;

但我得到以下异常:

org.apache.jasper.JasperException: javax.el.ELException: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: domein.Student.dossiers, no session or session was closed

当我将达析报告的 FetchType 设置为 Eager 时，我什至无法运行我的项目:

Severe:   Exception while loading the app : java.lang.IllegalStateException: ContainerBase.addChild: start: org.apache.catalina.LifecycleException: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in ServletContext resource [/WEB-INF/dispatcher-servlet.xml]: Invocation of init method failed; nested exception is javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build EntityManagerFactory

当我用谷歌搜索时，我找到了以下解决方案:

@RequestMapping(value = "/detail", method = RequestMethod.GET)
    public String detail(Model model, Principal principal, @RequestParam("id") int id) { 
        Presentatie p = presentatieDao.get(id);
        Hibernate.initialize(p.getStudent().getDefinitiefDossier().getVoorstel().getTitel());
        model.addAttribute("presentatie", p);
        return "detail";
}

但它再次给了我以下异常:

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: domein.Student.dossiers, no session or session was closed

Answer 1

您的 Controller 没有数据库上下文，因此他不可能获取所有延迟加载数据。您需要做的是直接在 Model 对象(可能是presentatieDao DAO)中编写一个方法，并在将其放入 Controller 之前，通过该方法将所有元素添加到列表中。