在Spring JSP页面中使用集合时，休眠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
}

评估部件是从评估实体延迟加载的。我也有弹簧控制器方法，它是数据库的事务和负载评估部分：

@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
}

将评估部分添加到Spring模型图后，它们将在我的JSP页面中可用，并且我正在使用JSTL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

如果此集合已在事务中加载，怎么办？我只是试图遍历，hibernate状态此时不应该加载任何东西，因为它已经被加载了。为什么发生这种奇怪的事情？

Answer 1

在视图中，entitymanager已关闭，因此集合中的元素无法在其中检索属性。您在控制器中编写的代码不会初始化集合中的元素（这是一个LAZY集合），而只会初始化集合（而不是其中的元素）。

通过OpenEntityManagerInViewFilter在您的Web配置中配置，可以强制entitymanager保持打开状态。

或更改您的控制器代码以包含一个调用Hibernate.initialize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
}

要么创建一个自定义查询，以强制获取集合。