I think i’m missing something fundamental about how Hibernate works, specifically with lazy loading. My problem is debugging, as I’m not sure if this is a Hibernate problem or a Spring problem in disguise. I thought I would ask here before doing some major refactoring.
I have two Entities. One holds a collection of the other in a OneToMany relationship. For my web page I wish to grab all of the first entity, and subsequently grab the set of associated entities for each and display them.
I believe my problem is this: I use a JpaTemplate to find all entities. This works fine, however because of Lazy loading I do not get the associated set of related entities. In my view (jsp) I want access to this set, but of course it is null because it is being lazy loaded. Now, i’m getting a LazyInitialization exception stating that the transaction has ended. To me this makes sense, of course the transaction should be over by now. The thing is, how can the assoicated set ever be lazy loaded if the transaction is over?
Entity Classes:
@Entity
public class LearningEntry implements Serializable {
private Long id;
String imagePath = "";
Set<Sample> samples = null;
//------------------------------
// Constructors
//------------------------------
public LearningEntry(){
imagePath = "";
samples = new HashSet<Sample>();
}
//------------------------------
// Instance Methods
//------------------------------
public void addSample(Sample s){
samples.add(s);
}
public void removeSample(Sample s){
samples.remove(s);
}
//------------------------------
// Setters and Getters
//------------------------------
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
//@Column(name = "wisi_LE_IMAGEPATH", length = 100, nullable = false)
public String getImagePath() {
return imagePath;
}
public void setImagePath(String imagePath) {
this.imagePath = imagePath;
}
// TODO - ONly works with fetch type EAGER
//@OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST, CascadeType.MERGE})
@OneToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
public Set<Sample> getSamples() {
return samples;
}
public void setSamples(Set<Sample> samples) {
this.samples = samples;
}
}
Sample Entity
@Entity
public class Sample implements Serializable {
private Long id;
Date creationDate;
String audioFileLocation;
Integer votes;
String description;
public Sample(){
creationDate = new Date();
audioFileLocation = "";
votes = 0;
description = "";
}
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getAudioFileLocation() {
return audioFileLocation;
}
public void setAudioFileLocation(String audioFileLocation) {
this.audioFileLocation = audioFileLocation;
}
@Temporal(TemporalType.DATE)
public Date getCreationDate() {
return creationDate;
}
public void setCreationDate(Date creationDate) {
this.creationDate = creationDate;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public Integer getVotes() {
return votes;
}
public void setVotes(Integer votes) {
this.votes = votes;
}
}
DAO Classes:
LearningEntryDAO
@Transactional
public class JpaLearningEntryDAO implements LearningEntryDAO{
private JpaTemplate jpaTemplate;
public JpaLearningEntryDAO(){
}
public void setJpaTemplate(JpaTemplate jpaTemplate){
this.jpaTemplate = jpaTemplate;
}
@Override
//@Transactional
public void delete(Long leId) {
LearningEntry dp = jpaTemplate.find(LearningEntry.class, leId);
jpaTemplate.remove(dp);
}
@Override
@SuppressWarnings("unchecked")
//@Transactional
public List<LearningEntry> findAll() {
return jpaTemplate.find("from LearningEntry");
}
@Override
//@Transactional
public LearningEntry findById(Long leId) {
return jpaTemplate.find(LearningEntry.class, leId);
}
@Override
//@Transactional
public LearningEntry store(LearningEntry dp) {
return jpaTemplate.merge(dp);
}
@Override
@SuppressWarnings("unchecked")
//@Transactional
public void deleteAll(){
throw new RuntimeException("deleteAll not implemented");
}
}
Sample DAO
@Transactional
public class JpaSampleDAO implements SampleDAO{
private JpaTemplate jpaTemplate;
public JpaSampleDAO(){}
public void setJpaTemplate(JpaTemplate jpaTemplate){
this.jpaTemplate = jpaTemplate;
}
@Override
//@Transactional
public void delete(Long sampleId) {
Sample dp = jpaTemplate.find(Sample.class, sampleId);
jpaTemplate.remove(dp);
}
@Override
@SuppressWarnings("unchecked")
public List<Sample> findAll() {
return jpaTemplate.find("from Sample");
}
@Override
public Sample findById(Long sampleId) {
return jpaTemplate.find(Sample.class, sampleId);
}
@Override
public Sample store(Sample dp) {
return jpaTemplate.merge(dp);
}
@Override
@SuppressWarnings("unchecked")
public void deleteAll(){
throw new RuntimeException("deleteAll not implemented");
}
}
Controller
@RequestMapping(value = "/index.htm", method = RequestMethod.GET)
public ModelAndView sayHello(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
Map<String, Object> model = new HashMap<String, Object>();
List<LearningEntry> le = learningEntryService.getLearningEntries();
model.put("learningEntries", le);
return new ModelAndView("main", model);
}
View
<section id="content" class="body">
<ol id="posts-list" class="hfeed">
<c:forEach items="${learningEntries}" var="learningEntry">
<li>
<table class="wisiEntry">
<tr>
<td class="pictureCell">
<img class="wisiEntry-pic" src="${learningEntry.imagePath}" />
</td>
<td class="previousNextCell"
<div class="wisiEntry-nextSampleButton">Next</div>
<div class="wisiEntry-previousSampleButton">Previous</div>
<br />
<div class="wisiEntry-addTagButton">Tag</div>
<div class="wisiEntry-addCommentButton">Comment</div>
<br />
<div class="wisiEntry-uploadButton">Upload</div>
</td>
<td>
<!-- ERROR HAPPENS HERE. Samples should not be null -->
<c:forEach items="${learningEntry.samples}" var="sample" varStatus = "status">
<table class="sampleEntry" ${status.first ? '' : 'style = "display:none"'}>
<tr>
<td class="sampleCell">
<p class="description">
${sample.description}
</p>
<audio src="${sample.audioFileLocation}" controls>
Your browser does not support the <code>audio</code> element.
</audio>
</td>
<td class="voteCell">
<img class="upVote" src="/images/upArrow.jpeg" />
<span class="voteNumber">${sample.votes}</span>
<img class="downVote" src="/images/downArrow.jpeg" />
</td>
</tr>
</table>
</c:forEach>
</td>
</tr>
</table>
</li>
</c:forEach>
</ol><!-- /#posts-list -->
</section><!-- /#content -->
Thanks to Vinegar for providing a working answer (upvoted).
I decided to add this answer that has also worked for me. I took this approach because I may want to make separate ajax calls in the future. In other words, I can ask for the LearningEntry in one transaction, than ask for its samples some time down the road.