I just started working with Java for web and I have this basic Quizz project where I integrated ajax.
In spring I have a controller which returns a list of answer objects based on a question id.
#RequestMapping(value = "/view-answers/{id}", method = RequestMethod.GET, produces = "application/json")
#SuppressWarnings("unchecked")
public #ResponseBody List<Answer> viewAnswers(#PathVariable int id, Model model){
// TODO: Get all quizzes
List<Answer> answers = answerService.findByQuestionId(id);
return answers;
}
Using this ajax fuction I retrieve the data from the controller with only one problem: It gets only the first object in full and the rest of the objects are just ID`s of the objects.
// DO GET
function ajaxGet(){
var questionID = $(".questionID").val();
$.ajax({
type : "GET",
url : "/view-answers/"+questionID,
dataType: 'json',
headers: {
Accept: 'application/json'
},
success: function(answers){
$('#answersList .answersUl').empty();
var ansList = "";
console.log(answers);
$.each(answers, function(i, answer){
var answer = i + "." + answer.answer + "<br />";
$('#answersList .answersUl ').append(answer);
});
console.log("Success: ", answers);
},
error : function(e) {
$("#getResultDiv").html("<strong>Error! Something went wrong.</strong>");
console.log("ERROR: ", e);
}
});
}
It can be a problem with my controller function? The findByQuestionId function is this:
#Override
public List<Answer> findByQuestionId(int question_id) {
Session session = sessionFactory.openSession();
session.beginTransaction();
Question question = session.find(Question.class, question_id);
List<Answer> answers = question.getAnswers();
session.getTransaction().commit();
//Close the session
session.close();
return answers;
}
This is what I'm getting with ajax right now:
The important part of my entities:
Quizz:
#Entity
#JsonIdentityInfo(
generator = ObjectIdGenerators.PropertyGenerator.class,
property = "quizz_id")
public class Quizz {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int quizz_id;
private String title;
private String description;
private int nr_participanti;
private int timp_disp;
private int nr_intrebari;
#OneToMany(mappedBy = "quizz", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#Fetch(value = FetchMode.SUBSELECT)
private List<Question> questions;
Question:
#Entity
#JsonIdentityInfo(
generator = ObjectIdGenerators.PropertyGenerator.class,
property = "id")
public class Question {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String titlu;
#ManyToOne
private Quizz quizz;
#OneToMany(mappedBy = "question", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#Fetch(value = FetchMode.SUBSELECT)
private List<Answer> answers;
Answer:
#Entity
#JsonIdentityInfo(
generator = ObjectIdGenerators.PropertyGenerator.class,
property = "answer_id")
public class Answer {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int answer_id;
private String answer;
private boolean corect;
#ManyToOne
private Question question;
I assume that it's a problem of lazy loading the related Answer objects in your service bean. Since you seem to use Hibernate the list of answers returned by question.getAnswers() may not eagerly fetch all answers related to the question. Hibernate loads one-to-many relations lazily by default. You close the Hibernate session at the end of the service method findByQuestionId and therefore it is not possible to load the remaining answers as soon as the list is iterated on when generating the response of the controller.
You could try the following in your service:
List<Answer> answers = question.getAnswers();
List<Answer> loadedAnswers = answers.stream().collect(Collectors.toList());
This will iterate the list of answers returned for the question relation immediately and add all answers to another transient list. Then it is safe to close the Hibernate session afterwards.
For anyone that has the same problem or somehow finds this question. The problem was indeed in my Entities.
For each entity I had to add two annotations:
#JsonManagedReference is the forward part of reference – the one that gets serialized normally.
#JsonBackReference is the back part of reference – it will be omitted from serialization.
Therefore, I annotate ManyToOne objects with #JsonManagedReference and OneToMany lists objects with #JsonBackReference. This was the only part that was missing in order for this to work.
Related
I want to load all objects from a table without a lazy objects/children and list them on the page (Thymeleaf template), but I get a LazyInitializationException every time. I tried to convert Hibernate entity objects into a POJO that doesnt contains a lazy/unwanted object but with the same result. I also tried open-in-view parameter set to false...
Simple example:
Parent:
#Entity
public class DocumentDbe implements Serializable {
public DocumentDbe(){
}
#Id
#Column(name = "id", updatable = false, nullable = false)
private Long id;
#OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.PERSIST)
private DocumentFileDbe documentFile;
....
}
Child:
#Entity
public class DocumentFileDbe implements Serializable {
public DocumentFileDbe(){}
#Id
#Column(name = "id", updatable = false, nullable = false)
private Long id;
#Column
#Lob
private byte[] documentData;
...
}
POJO:
public class DocumentDto implements Serializable {
public DocumentDto(){
}
public DocumentDto(DocumentDbe doc){
this.id = doc.getId();
}
....
}
Controller:
#GetMapping("/list")
String getList(Model model) {
List<DocumentDbe> docs;
List<DocumentDto> data = new ArrayList<>();
try (Session ses = sessionFactory.openSession()) {
docs = ses.createQuery("FROM DocumentDbe").list();
docs.forEach(doc -> {
data.add(new DocumentDto(doc));
});
}
model.addAttribute(MODEL_LIST_DATA, data);
return "list";
}
EDIT: Thrown exception:
org.thymeleaf.exceptions.TemplateInputException: An error happened during template parsing (template: "class path resource [templates/list.html]")] with root cause
org.hibernate.LazyInitializationException: could not initialize proxy - no Session
EDIT2:
In DocumentDbe is relation with another object (EAGER this time so I was not paying attention to it) , which has reference to DocumentDbe again.. chained relationship and LazyInitializationException is created...
EDIT3:
Although
This is modified and working controller, without POJO:
#GetMapping("/list")
String getList(Model model) {
List<DocumentDbe> docs;
try (Session ses = sessionFactory.openSession()) {
docs = ses.createQuery("FROM DocumentDbe ORDER BY id DESC").list();
docs.forEach(doc -> {
doc.setDocumentFile(null);
doc.getHistory().forEach(log ->{
log.setDocument(null);
});
});
}
model.addAttribute(MODEL_ADMIN_DATA, docs);
return "list";
}
In class DocumentDbe you have mark relation as Lazy. In default relation #ManyToOne and #OneToOne is as EAGER, so if you don't want Lazy, you have to change
#OneToOne(cascade = CascadeType.PERSIST)
If you want have #lob also as eager:
#Lob
#Basic( fetch = FetchType.EAGER )
I am getting this A collection with cascade="all-delete-orphan" was no longer referenced by the owning entity instance error with my oneToMany relationship when trying to update my child element (report). Although I see this question asked a few times here, I haven't been able to make my code to work with them and I now feel it may be an issue with me using Lombok perhaps, since most of the answers here mention about changes on the hashcode and equals methods, which are abstracted away by Lombok? I tried to remove Lombok to try without it but then I got a bit confused on what to do next. If I could get some guidance on how to fix this issue within my original Lombok implementation please.
#Entity
#Table(name = "category")
#AllArgsConstructor
#NoArgsConstructor
#Data
public class Category {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private UUID id;
#Column(name = "category_title", nullable = false)
private String title;
#OneToMany(mappedBy = "category", cascade = CascadeType.ALL, orphanRemoval = true)
private Collection<Report> report;
public Category(UUID id, String title) {
this.id = id;
this.title = title;
}
}
#NoArgsConstructor
#AllArgsConstructor
#Entity
#Table(name = "report")
#Data
public class Report {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private UUID id;
#Column(name = "report_title", nullable = false)
private String reportTitle;
#ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.MERGE)
#JoinColumn(name = "category_id", nullable = false)
private Category category;
public Report(UUID id) {
this.id = id;
}
}
#Override
public ReportUpdateDto updateReport(UUID id, ReportUpdateDto reportUpdateDto) {
if (reportRepository.findById(id).isPresent()) {
Report existingReport = reportRepository.findById(id).get();
existingReport.setReportTitle(reportUpdateDto.getTitle());
Category existingCategory = categoryRepository.findById(reportUpdateDto.getCategory().getId()).get();
Category category = new Category(existingCategory.getId(), existingCategory.getTitle());
existingReport.setCategory(category); // This is needed to remove hibernate interceptor to be set together with the other category properties
Report updatedReport = reportRepository.save(existingReport);
updatedReport.setCategory(category); // This is needed to remove hibernate interceptor to be set together with the other category properties
ReportUpdateDto newReportUpdateDto = new ReportUpdateDto(updatedReport.getId(),
updatedReport.getReportTitle(), updatedReport.getCategory());
return newReportUpdateDto;
} else {
return null;
}
}
Thank you very much.
Fast solution (but not recommended)
The error of collection [...] no longer referenced arrises in your code beacuse the synchronization between both sides of the bidiretional mapping category-report was just partially done.
It's important to note that binding the category to the report and vice-versa is not done by Hibernate. We must do this ouserselves, in the code, in order to sync both sides of the relationship, otherwise we may break the Domain Model relationship consistency.
In your code you have done half of the synchronization (binding the category to the report):
existingReport.setCategory(category);
What is missing is the binding of the report to the category:
category.addReport(existingReport);
where the Category.addReport() may be like that:
public void addReport(Report r){
if (this.report == null){
this.report = new ArrayList<>();
}
this.report.add(r);
}
Recommended Solution - Best practice for synchronizing both sides of the mapping
The suggested code above works, but it is error prone as the programmer may forget to call one of the lines when updating the relationship.
A better approach is to encapsulate that sychronization logic in a method in the owning side of the relationship. And that side is the Category as stated here: mappedBy = "category".
So what we do is to encapsulate in the Category.addReport(...) all the logic of cross-reference between Category and Report.
Considering the above version of addReport() method, what is missing is adding r.setCategory(this).
public class Category {
public void addReport(Report r){
if (this.reports == null){
this.reports = new ArrayList<>();
}
r.setCategory(this);
this.reports.add(r);
}
}
Now, in the updateReport() it is enough to call the addReport() and the commented line bellow can be deleted:
//existingReport.setCategory(category); //That line can be removed
category.addReport(existingReport);
It is a good practice including in Category a removeReport() method as well:
public void removeReport(Report r){
if (this.reports != null){
r.setCategory = null;
this.reports.remove(r);
}
}
That is the code of Category.java after the two methods were added:
public class Category {
#OneToMany(mappedBy = "category", cascade = CascadeType.ALL, orphanRemoval = true)
private Collection<Report> reports;
//Code ommited for brevity
public void addReport(Report r){
if (this.reports == null){
this.reports = new ArrayList<>();
}
r.setCategory(this);
this.reports.add(r);
}
public void removeReport(Report r){
if (this.reports != null){
r.setCategory = null;
this.reports.remove(r);
}
}
}
And the code for updating a report category now is this:
public ReportUpdateDto updateReport(UUID id, ReportUpdateDto reportUpdateDto) {
if (reportRepository.findById(id).isPresent()) {
Report existingReport = reportRepository.findById(id).get();
existingReport.setReportTitle(reportUpdateDto.getTitle());
Category existingCategory = categoryRepository.findById(reportUpdateDto.getCategory().getId()).get();
existingCategory.addReport(existingReport);
reportRepository.save(existingReport);
return new ReportUpdateDto(existingReport.getId(),
existingReport.getReportTitle(), existingReport.getCategory());
} else {
return null;
}
}
A good resource to see a practical example of synchronization in bidirectional associations: https://vladmihalcea.com/jpa-hibernate-synchronize-bidirectional-entity-associations/
Lombok and Hibernate - not the best of the combinations
Though we can not blame Lombok for the error described in your question, many problems may arrise when using Lombok alongside with Hibernate:
Properties being loaded even if marked for lazy loading...
When generating hashcode(), equals() or toString() using Lombok, the getters of fields marked as lazy are very likelly to be called. So the programmer's initial intention of postponing some properties loading will no be respected as they will be retrieved from the database when one of hascode(), equals() or toString() is invoked.
In the best case scenario, if a session is open, this will cause additional queries and slow down your application.
In the worst case scenarios, when no session is available, a LazyInitializationException will be thrown.
Lombok's hashcode()/equals() affecting the bevahior of collections
Hibernate uses hascode() and equals() logic to check if a object is order to avoid inserting the same object twice. The same applies to removing from a list.
The way Lombok generates the methods hashcode() and equals() may affect hibernate and create inconsistent properties (especially Collections).
See this article for more info on this subject: https://thorben-janssen.com/lombok-hibernate-how-to-avoid-common-pitfalls/
Lombok/Hibernate integration in a nutshell
Don't use Lombok for entity classes. Lombok annotations you need to avoid are #Data, #ToString, and #EqualsAndHashCode.
Off-topic - Beware of delete-orphan
In Category, the #OneToMany mapping is defined with orphanRemoval=true as bellow:
#OneToMany(mappedBy = "category", cascade = CascadeType.ALL, orphanRemoval = true)
private Collection<Report> reports;
The orphanRemoval=true means that when deleting a category, all the reports in that category will be deleted as well.
It is important to assess if that is the desired behavior in your application.
See an example of the SQLs hibernate will execute when calling categoryRepository.delete(category):
//Retrieving all the reports associated to the category
select
report0_.category_id as category3_1_0_,
report0_.id as id1_1_0_,
report0_.id as id1_1_1_,
report0_.category_id as category3_1_1_,
report0_.report_title as report_t2_1_1_
from
report report0_
where
report0_.category_id=?
//Deleting all the report associated to the category (retrieved in previous select)
delete from
report
where
id=?
//Deleting the category
delete from
category
where
id=?
Just an update based on the accepted answer to avoid a StackOverflow and circular loop that came up after the changes.
I had to create a new Category object to remove the reports inside it within my return dto, otherwise as the category contains that same report, that again contains that category and so on, the infinite loop could be seen on my response.
#Override
public ReportUpdateDto updateReport(UUID id, ReportUpdateDto reportUpdateDto) {
if (reportRepository.findById(id).isPresent()) {
Report existingReport = reportRepository.findById(id).get();
existingReport.setReportTitle(reportUpdateDto.getTitle());
Category existingCategory = categoryRepository.findById(reportUpdateDto.getCategory().getId()).get();
Category category = new Category(existingCategory.getId(), existingCategory.getTitle());
existingCategory.addReport(existingReport);
reportRepository.save(existingReport);
return new ReportUpdateDto(existingReport.getId(),
existingReport.getReportTitle(), existingReport.getRun_date(),
existingReport.getCreated_date(), category);
} else {
return null;
}
}
So added this part:
Category existingCategory = categoryRepository.findById(reportUpdateDto.getCategory().getId()).get();
Category category = new Category(existingCategory.getId(), existingCategory.getTitle());
existingCategory.addReport(existingReport);
As if I have something like
Category category = new Category(existingCategory.getId(), existingCategory.getTitle(), existingCategory.getReports);
I can see the issue once again, which is what the existingCategory object itself contains.
And here my final entities
#NoArgsConstructor
#AllArgsConstructor
#Entity
#Table(name = "report")
#Data
public class Report {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private UUID id;
#Column(name = "report_title", nullable = false)
private String reportTitle;
#ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.MERGE)
#JoinColumn(name = "category_id", nullable = false)
private Category category;
#Entity
#Table(name = "category")
#AllArgsConstructor
#NoArgsConstructor
#Data
public class Category {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private UUID id;
#Column(name = "category_title", nullable = false)
private String title;
#OneToMany(fetch = FetchType.LAZY, mappedBy = "category", cascade = CascadeType.ALL, orphanRemoval = true)
private Collection<Report> reports;
public Category(UUID id, String title) {
this.id = id;
this.title = title;
}
public void addReport(Report r) {
if (this.reports == null) {
this.reports = new ArrayList<>();
}
r.setCategory(this);
this.reports.add(r);
}
public void removeReport(Report r) {
if (this.reports != null) {
r.setCategory(null);
this.reports.remove(r);
}
}
}
I have two entities defined. Both of them are connected through a bidirectional #OneToMany.
Here are my two entities
#Entity(name = "Post")
#Table(name = "post")
public class Post {
#Id
#GeneratedValue
private Long id;
private String title;
#OneToMany(
mappedBy = "post",
cascade = CascadeType.ALL,
orphanRemoval = true
)
private List<PostComment> comments = new ArrayList<>();
//Constructors, getters and setters removed for brevity
public void addComment(PostComment comment) {
comments.add(comment);
comment.setPost(this);
}
public void removeComment(PostComment comment) {
comments.remove(comment);
comment.setPost(null);
}
}
#Entity(name = "PostComment")
#Table(name = "post_comment")
public class PostComment {
#Id
#GeneratedValue
private Long id;
private String review;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "post_id")
private Post post;
//Constructors, getters and setters removed for brevity
#Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof PostComment )) return false;
return id != null && id.equals(((PostComment) o).getId());
}
#Override
public int hashCode() {
return Objects.hash(id);
}
}
I am using Spring Data JPA to fetch / save entities.
Saving works fine and for example if I save 1 post and 4 post comments I can see the entries in the database. The database I am using is PostgreSQL.
When I am fetching all the posts through my repository using the findAll method, then I receive the post with the 4 comments.
The issue is when I am fetching only one post through the getOne method, the post is found, but for some reason the entity contains 7 post comments. The first entry is duplicated 3 times and the second one is duplicated two times.
I don't understand why this is happening and how can I fix this.
Any help is appreciated.
Thanks
You need to change List to Set.
#OneToMany(mappedBy = "post",cascade = CascadeType.ALL,orphanRemoval = true)
private Set<PostComment> comments = new HashSet<>();
I have a small example with some get/post mappings and JpaRepository calls in Spring Boot.
Firstly I have two entity Classes:
#Entity
#Table(name = "stock")
public class Stock extends BaseEntity
{
#Column(name = "value")
public String value;
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
#Entity
#Table(name = "stock_item")
public class StockItem extends BaseEntity
{
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "stock_id", insertable = false, updatable = false)
public Stock stock;
#Column(name = "stock_id")
public Long stockId;
#Column(name = "value")
public String value;
}
I have a many-to-one association from StockItem to Stock.
I insert a Stock and have a controller as below:
#Autowired
public Controller(StockItemRepository stockItemRepository) {
this.stockItemRepository = stockItemRepository;
}
#RequestMapping("/")
#Transactional(readOnly = true)
public String get() {
List<StockItem> stockItemList = stockItemRepository.getItemsById(1L);
System.out.println("TX MANAGER: " + TransactionSynchronizationManager.isActualTransactionActive());
for (StockItem stockItem : stockItemList) {
System.out.println(stockItem.getStock().getValue());
}
return "get";
}
#RequestMapping("/fromSave")
#Transactional
public String post() {
StockItem stockItem = new StockItem();
stockItem.setStockId(1L);
stockItemRepository.saveAndFlush(stockItem);
System.out.println("saveCalled");
return get();
}
and getItemsById in the repository is defined as follows:
#Query("FROM StockItem si " +
"JOIN FETCH si.stock stk " +
"WHERE si.stockId = :id")
List<StockItem> getItemsById(#Param("id") Long id);
From my understanding, when I call the post method:
it creates a new item
sets the id of the associated attribute
saves and ends the transaction
Heres where things get strange...
I call get after the post and make the above repository call, which has a join fetch and when I call stockitem.getStock().getValue() I get a null pointer when I expect a LazyInitializationException.
If I call the get() from the mapping, outside the class, it successfully loads the associated object.
I have even removed the #Transaction annotation from the get, as well as
the join-fetch from my query and again, if I call from outside of the class it works and from the post, it crashes with a NullPointerException.
I have put the get inside of a TransactionTemplate.execute() and I still get a NullPointerException when calling from inside the class.
So the main questions are:
Why am I getting a NullPointerException instead of LazyInitializationException?
What is the transaction magic behind having no transaction but successfully fetching a lazy attribute??
The problem here is that you are misusing JPA. As you are seemingly aware judging from the comments on the other answer you have mapped the stock_id column twice. Once as a many-to-one relationship
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "stock_id", insertable = false, updatable = false)
public Stock stock;
and once as a simple column
#Column(name = "stock_id")
public Long stockId;
When you set the simple column and flush the changes as in your post() method the following happens:
the value gets set in the simple column. The reference is still null.
the value gets stored in the database. The reference is still null.
The repository call will find the id of the StockItemin the Persistence Context and return that instance, i.e. the exact same used in the post method, with the reference still null.
What is the transaction magic behind having no transaction but successfully fetching a lazy attribute??
No magic involved here. fetch specifications are only used for object traversal. JPQL queries don't honor these.
The unasked question remains: how to fix the situation?
The obvious fix is to lose the simple column and just use entity references as intended by JPA.
You don't want to do that in order to avoid DB access somewhere. But as long as you only access the id of the referenced Stock it shouldn't get initialized. So it seems that this should be possible with just Lazy Fetching.
Alternatively, I'd suggest removing the many-to-one relationship and creating a repository for Stock and manually loading it when required.
#Entity
#Table(name = "stock_item")
public class StockItem extends BaseEntity
{
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "stock_id", insertable = false, updatable = false) //here is your problem
public Stock stock;
#Column(name = "stock_id")
public Long stockId; // why explicitly define a separate column for foreign key after mapping it above
#Column(name = "value")
public String value;
}
with insertable = false and updatable = false it won't insert in your DB and neither it will allow updation, so you are getting NullPointerException. You should atleast allow insertion in order to run the query based on the foreign key stock_id
UPDATE
Change your Entity class with property-based access:
#Entity
#Table(name = "stock_item")
public class StockItem extends BaseEntity
{
private Stock stock; // variables should always be private since you have getters and setters
private String value;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "stock_id", updatable = false)
public Stock getStock() {
return stock;
}
public void setStock(Stock stock) {
this.stock = stock;
}
#Basic
#Column(name = "value")
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
I have a project with Spring Boot, and I cannot make lazy loading work. I have 2 entities: Question and Answer. A question can have many answers.
What I want is, when I try to get an answer, to get only the answer without the question. And also, if I want both, to have this possibility.
What I did, is I added in application.yml: spring.jpa.open-in-view: true.
The Answer entity is like:
#Entity
#Table(name = "mst_ans_answer", schema = "lquest_sc")
public class Answer implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "lquest_sc.mst_ans_answer_ans_lqs_id_seq")
#SequenceGenerator( name = "lquest_sc.mst_ans_answer_ans_lqs_id_seq", sequenceName = "lquest_sc.mst_ans_answer_ans_lqs_id_seq")
#Column(name = "ans_lqs_id")
private int id;
#Column(name = "qst_lqs_id")
private int questionId;
#Column(name = "ans_text")
private String text;
#ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = false)
#JoinColumn(name = "qst_lqs_id", insertable=false, updatable=false)
#JsonIgnore
private Question question;
//getters and setters
}
The Question entity is:
#Entity
#Table(name = "mst_qst_question", schema = "lquest_sc")
public class Question implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "lquest_sc.mst_qst_question_qst_lqs_id_seq")
#SequenceGenerator(name = "lquest_sc.mst_qst_question_qst_lqs_id_seq", sequenceName = "lquest_sc.mst_qst_question_qst_lqs_id_seq")
#Column(name = "qst_lqs_id")
private int id;
#Column(name = "qst_title")
private String title;
#OneToMany(fetch = FetchType.LAZY, mappedBy = "question")
#OrderBy("order asc")
private Set<Answer> answers = new HashSet<Answer>();
//getters and setters here
The call in the controller is:
#RequestMapping(value = "/questionId/{id}", method = RequestMethod.GET)
public List<Answer> listAll( #PathVariable("id") int id ){
List<Answer> answers = answerRepository.findByEnabledAndQuestionIdOrderByOrderAsc(1,id);
return answers;
}
and the repository is
public interface AnswerRepository extends JpaRepository<Answer, Long> {
List<Answer> findByEnabledAndQuestionIdOrderByOrderAsc(int enabled,int questionId);
}
The problem is that in the controller, when I try to evaluate
answers.get(0).getQuestion(), I receive the entity of Question, with the properties filled with null values and the error Method threw 'org.hibernate.LazyInitializationException' exception. Cannot evaluate Question_$$_jvst5b6_1.toString(). What am I doing wrong?
I don't know why spring.jpa.open-in-view = true is not working in your case. Maybe the OpenEntityManagerInViewInterceptordoes not get triggered or the thread has been left, when you are evaluating the Question. Or you have an older version which just does not support it.
Lazy loading works only inside of a transaction. A solution could be -
as #Pradeep already gave you the hint - to use #Tranactional inside a business logic class.
Even if you put the #Transactional inside your repository it will not work, because you have to put the annotation on top of the method where you are trying to evaluate answers.get(0).getQuestion().
Furthermore I advise you not to call your repository from the controller directly, but to use a service layer, where you put your business logic.
Example implementation
This is only a example implementation to show you how to structure your application and what the important keywords are. Also note, that you can either use #Inject or #Autowired. When you have implemented your logic, just inject the service into your controller and use it there.
AnswerService.java
public interface AnswerService {
List<Answer> findByEnabledAndQuestionIdOrderByOrderAsc(int enabled, Long id);
}
AnswerServiceImpl.java
#Service
public class AnswerServiceImpl implements AnswerService {
private AnswerRepository answerRepository;
#Inject
public AnswerServiceImpl(AnswerRepository answerRepository) {
this.answerRepository = answerRepository;
}
#Transactional
#Override
public List<Answer> findByEnabledAndQuestionIdOrderByOrderAsc(int enabled, Long id) {
List<Answer> answerList = findByEnabledAndQuestionIdOrderByOrderAsc(int enabled,int questionId);
// do your lazy loading here
// because you are still in the same transactional context
// return the list
return answerList;
}
}