Springboot - list of objects with child entities not returned - spring-boot

Question

I have this object named SubmittedQuiz, it consists of a Quiz object, User object and submittedQuestions object.
When I try to do this request:
GET http://localhost:8080/SubmittedQuiz/getForUser/10
I get returned the following error:
Type definition error: [simple type, class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.ArrayList[0]->edowl.Model.SubmittedQuiz["user"]->edowl.Model.User$HibernateProxy$lNsgwyQb["hibernateLazyInitializer"])"
The request finds the objects fine, when setting breakpoints it actually gets the list of objects however it fails on the return statement.
The controller method is as shown below:
#GetMapping("/getForUser/{id}")
public ResponseEntity<List<SubmittedQuiz>> getSubmittedQuizForUser(#PathVariable("id") Long id){
List<SubmittedQuiz> quizzes = submittedQuizService.findAllByUserId(id);
return new ResponseEntity<>(quizzes, HttpStatus.OK); //ok is 200 status code
}
The Service is shown below:
public List<SubmittedQuiz> findAllByUserId(Long id) {
return submittedQuizRepo.findAllByUserId(id);
}
The Repo is shown below:
List<SubmittedQuiz> findAllByUserId(Long id);
The SubmittedQuiz is shown below:
#Entity
#Table(name = "Submitted_Quiz")
public class SubmittedQuiz {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#ManyToOne(fetch = FetchType.LAZY)
#JoinTable(name = "User_Quiz_Submitted",
joinColumns = { #JoinColumn(name = "quiz_submitted_id")},
inverseJoinColumns = { #JoinColumn(name = "user_id")})
public User user;
#ManyToOne(fetch = FetchType.LAZY)
#JoinTable(name = "Quiz_Quiz_Submitted",
joinColumns = { #JoinColumn(name = "quiz_submitted_id")},
inverseJoinColumns = { #JoinColumn(name = "quiz_id")})
public Quiz quiz;
private float score;
private LocalDate generatedDate;
private float timeTaken;
#OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
#JoinTable(name = "quiz_submitted_question",
joinColumns = { #JoinColumn(name = "quiz_submitted_id")},
inverseJoinColumns = { #JoinColumn(name = "question_id")})
#Column(name = "submitted_questions")
private Set<SubmittedQuestion> submittedQuestions = new HashSet<>();
I saw one suggestion about putting #JsonBackReference & #JsonManagedReference annotations on the objects.
However I haven't needed to do this on any other object thus far and the current annotations I have used sufficed fine till this point
Are there any suggestions?

Answer 1

You could try to use EntityGraph for this purpose.
And set to atributePaths all entities which have FetchType.LAZY:
#EntityGraph(attributePaths = {"user", "quiz", "submitted_questions"})
List<SubmittedQuiz> findAllByUserId(Long id);
Some hint for controller - you don't need to set 200 response directly. Status code OK is returned by default. So following will be fine:
#GetMapping("/getForUser/{id}")
public List<SubmittedQuiz> getSubmittedQuizForUser(#PathVariable("id") Long id){
return submittedQuizService.findAllByUserId(id);
}
UPDATE:
Try to add web configuration like::
#Configuration
public class WebMvcConfig implements WebMvcConfigurer {
#Bean
public Module datatypeHibernateModule() {
return new Hibernate5Module();
}
}
If it wouldn't help to solve the issue with the error try to add:
#JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
to all your subentities:
#ManyToOne(fetch = FetchType.LAZY)
#JoinTable(...)
#JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
public User user;
Also, JPA API requires that your entities have to be serializable.
You have to update it like follows:
public class SubmittedQuiz implements Serializable {
private static final long serialVersionUID = 1L;
Add the same for other entities as well (User, Quiz...)