Spring Boot JPA StackOverflowError

Question

I am new at spring boot JPA. I am trying the examples described here:

https://en.wikibooks.org/wiki/Java_Persistence/OneToMany#Example_of_a_OneToMany_relationship_database

so I have defined the two entities:

@Entity
public class Employee {
  @Id
  @Column(name="EMP_ID")
  private long id;
  ...
  @OneToMany(mappedBy="owner")
  private List<Phone> phones;
  ...
}

and:

@Entity
public class Phone {
  @Id
  private long id;
  ...
  @ManyToOne(fetch=FetchType.LAZY)
  @JoinColumn(name="OWNER_ID")
  private Employee owner;
  ...
}

(an employee can have more than one phone number, work, home, etc.). The problem is that, when I try to list the Employee instances with my entityManager:

public List<Employee> getAll() 
{
    return entityManager.createQuery("from Employee").getResultList();
}

I got a spring StackOverflowError. Actually I am trying to refer Employee, which includes a list of Phone(s), but a Phone refers an Employee back so is it not a recursion? I feel as I am missing something about bi-directional associations (uni-directional associations worked fine) .. how can I have an entity A which refer B, being B referring A, and got a JSON response correctly from spring? Can someone point me in the right direction?

I found this workaround:

Infinite Recursion with Jackson JSON and Hibernate JPA issue

using @JsonManagedReference and @JsonBackReference I can tell Jackson not to serialize one side on my association and it works! But the final result is a unidirectional association (I can see the list of phones on the employee entity, but not the employee on every phone instance). So what is the purpose of bi-directional association if I have to cut one side of them in order to have my code working? Very confused :)

Answer 1

I believe Hibernate can manage this bi-directional association pretty well. It's only when Jackson tries to build the JSON from your object structure, it goes into recursion.

Answer 2

If you are using @Data in your entity then try to override the toString method.

I have faced the same issue but after overriding the toString method it got resolved. May be toString creates circular dependency while converting.