JPA issue (lazy loading? eager ?) - spring

Question

Iam building a simple Spring Boot app, with 2 entities:
- Student model
#Entity
#Data
#AllArgsConstructor
#NoArgsConstructor
public class Student {
#Id #GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private String password;
private boolean active;
private Date dob;
private String roles;
#ManyToOne
private Training training;
}
- Training model
#Entity
#Data
#AllArgsConstructor
#NoArgsConstructor
public class Training {
#Id #GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private int duration;
#OneToMany(mappedBy = "training")
#JsonIgnore
private Collection<Student> students;
}
EDIT
I run the app by adding 2 resources in the db:
public static void main(String[] args) {
SpringApplication.run(MsSchoolingSbApplication.class, args);
}
#Override
public void run(String... args) throws Exception {
Training t1=trainingRepo.save(new Training(null,"php", 20, null));
Training t2=trainingRepo.save(new Training(null,"java", 20, null));
Student st=new Student(null, "XXXX", "ZZZZ", true,new Date(),"ADMIN",t1);
Student st2=new Student(null, "XXXXX2", "ZZZZZ2", true,new Date(),"USER",t2);
studentRepo.save(st);
studentRepo.save(st2);
}
END EDIT
EDIT 2
- StudentRepo
#RepositoryRestController
public interface StudentRepo extends JpaRepository<Student, Long>{
public List<Student> findByNameStartsWith(String name);
Optional<Student> findByName(String name);
}
- TrainingRepo
#RepositoryRestController
public interface TrainingRepo extends JpaRepository<Training, Long> {
}
END EDIT 2
i've tried to put fetch = FetchType.EAGER or LAZY, i've also added #JsonIgnore but as soon as i fill the db with new data (trainings and students) and run the app, i get this message:
Caused by: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.schooling.models.Training.students, could not initialize proxy - no Session
What am i doing wrong ?

Answer 1

The problem you got must have related to how you use those 2 entities so you need to provide more information about how you use it.
You might want to look out for your problem in this tutorial: https://www.baeldung.com/hibernate-initialize-proxy-exception

Answer 2

Do not use Lombok's #Data annotation on #Entity classes.
Reason: #Data generates hashcode(), equals() and toString() methods that use the generated getters. Using the getter means of course fetching new data even if the property was marked with FetchType=LAZY.
Somewhere along the way hibernate tries to log the data with toString() and it crashes
EDIT
you can exclude the relation from the toString method by adding, for example in my case:
#ToString(exclude = {"students"})