在Spring JSP页面中使用集合时,hibernate LazyInitializationException
问题内容:
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?
问题答案:
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。