java - 在 Spring JSP 页面中使用集合时出现 Hibernate LazyInitializationException

Question

我有这样的实体:

@Entity
@Table(name = "ASSESSMENT")
public class Assessment {

    //All other fields..

    @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "assessment")
    @OrderBy(value = "order ASC")
    private List<AssessmentPart> assessmentParts = new LinkedList<>();

    public List<AssessmentPart> getAssessmentParts() {
        return assessmentParts;
    }

    //All other getters/setters
}

另一个:

@Entity
@Table(name = "ASSESSMENT_PART")
public class AssessmentPart {

    //All other fields

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "ASSESSMENT_ID", nullable = false)
    private Assessment assessment;

    public Assessment getAssessment() {
        return assessment;
    }

    public void setAssessment(Assessment assessment) {
        this.assessment = assessment;
    }

    //All other getters/setters
}

评估部分是从评估实体延迟加载的。我还有 spring Controller 方法，它是事务性的，并从数据库加载评估部分:

@Transactional
public void doSomething(String partId, Map<String, Object> model) {

    AssessmentPart assessmentPart = //laods a part with entity manager
    Assessment assessment = assessmentPart.getAssessment(); //Getting the assessments

    model.put("assessmentParts", assessment.getAssessmentParts()); //adding all assessments parts into spring model map
}

一旦我将评估部分添加到 spring 模型映射中，它们就可以在我的 JSP 页面中使用，我正在使用 JSTL 循环遍历它们:

<c:forEach var="assessmentPart" items="${assessmentParts}">
     //Not loading any lazy stuff, just getting an ID of assessment part
</c:forEach>

此 JSP 页面抛出异常:

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: my.package.something.Assessment.assessmentParts, could not initialize proxy - no Session

如果此集合已加载到事务中，这怎么可能？我只是想遍历，此时 hibernate 不应该加载任何东西，因为它已经加载了。为什么会发生这种奇怪的事情？

Answer 1

在 View 中，entitymanager 已经关闭，因此您集合中的元素无法检索那里的属性。您在 Controller 中编写的代码不会初始化集合中的元素(它是一个 LAZY 集合)，而只会初始化集合(而不是其中的元素)。

通过在您的 Web 配置中配置 OpenEntityManagerInViewFilter 强制实体管理器保持打开状态。

或者更改您的 Controller 代码以包含对 Hibernate.initialize 的调用以正确初始化您的集合。

@Transactional
public void doSomething(String partId, Map<String, Object> model) {

    AssessmentPart assessmentPart = //laods a part with entity manager
    Assessment assessment = assessmentPart.getAssessment(); //Getting the assessments
    Hibernate.initialize(assesment.getAssesmentParts()); // Init collection
    model.put("assessmentParts", assessment.getAssessmentParts()); //adding all assessments parts into spring model map
}

或者创建一个自定义查询，强制预先获取集合。