example41 - StackOverflow caused by bidirectional association w/ @Data

cased by Person.java and EazyClass.java

In a bidirectional association in JPA/Hibernate, having two entities reference each other can potentially lead to a stack overflow error if not handled correctly, especially when using Lombok's @Data annotation. The @Data annotation generates toString(), equals(), and hashCode() methods, which can cause issues with bidirectional relationships.

Why the Stack Overflow Occurs The stack overflow occurs because the generated toString(), equals(), and hashCode() methods can end up in an infinite loop. For example:

Entity A references Entity B. Entity B references Entity A. When toString() is called on Entity A, it calls toString() on Entity B, which in turn calls toString() on Entity A, and so on, leading to a stack overflow.

Solutions

1. Use @ToString.Exclude and @EqualsAndHashCode.Exclude By excluding the bidirectional field, you prevent the infinite loop in the toString(), equals(), and hashCode() methods.

Person.java

    @ManyToOne(fetch = FetchType.LAZY, optional = true)
    @JoinColumn(name = "class_id", referencedColumnName = "classId", nullable = true)
    @JsonBackReference
    @ToString.Exclude
    @EqualsAndHashCode.Exclude
    private EazyClass eazyClass;

EazyClass.java

    @OneToMany(mappedBy = "eazyClass", cascade = CascadeType.PERSIST,targetEntity = Person.class)
    @JsonManagedReference
    @ToString.Exclude
    @EqualsAndHashCode.Exclude
    private Set<Person> persons;

2. Manually Implement toString(), equals(), and hashCode()

Conclusion

When using bidirectional associations with Lombok's @Data annotation, it's crucial to prevent infinite recursion in the generated methods. You can achieve this by excluding the bidirectional fields from toString(), equals(), and hashCode() using @ToString.Exclude and @EqualsAndHashCode.Exclude, or by manually implementing these methods to avoid the recursion.

devYuraKim / spring

example41 - StackOverflow caused by bidirectional association w/ @Data #3