Hibernate5Module doesn't fetch OneToMany collection - spring

Question

First of all I have had two related entities mapped with bidirectional OneToMany:
#Data
#Entity
#Table(name = "tbl_parent")
public class Parent {
#Id
#Column(name = "parent_id")
private Long id;
...
#OneToMany(mappedBy = "parent")
private List<Child> children = new ArrayList<>();
}
and
#Data
#Entity
#Table(name = "tbl_child")
#ToString(exclude = "parent")
public class Child {
#Id
#Column(name = "child_id")
private Long id;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "parent_id")
private Parent parent;
}
However, I had StackOverFlow for method findAll() for Parent entity as far as infinite loop occurred during serialization.
Then I added property in application.yml:
spring:jsp:open-in-view: false
And had another problem with serialization. To solve it I added dependency in build.gradle:
implementation "com.fasterxml.jackson.datatype:jackson-datatype-hibernate5"
And configuration class:
#Configuration
public class JacksonConfiguration {
#Bean
public JavaTimeModule javaTimeModule() {
return new JavaTimeModule();
}
#Bean
public Jdk8Module jdk8TimeModule() {
return new Jdk8Module();
}
#Bean
public Hibernate5Module hibernate5Module() {
return new Hibernate5Module();
}
}
Now I have no error but list in parent entity is always null.
What I'm doing wrong? How can I fetch all related children entities without StackOverflow?

Answer 1

#Data annotation from Lombok can cause stackoverflows due to circular dependencies between classes if both classes have #Data and collections/toStrings mentioning each other.
See Lombok.hashCode issue with "java.lang.StackOverflowError: null"

Answer 2

The issue is quite simple: you cannot hope to serialize both sides of a bidirectional association. If you try to do that, you'll get a JSON representation of Parent with a children property, and each object in children will have a parent property, with each parent containing a children property, and so on, ad nauseam.
From what you describe, I'm assuming you want to opt out of serializing the parent property, in which case you should put #JsonIgnore on Child.parent.
Also, since you enabled the HibernateModule, which by default ignores lazy properties, you should either disable it, enable its FORCE_LAZY_LOADING feature, or configure Parent.children to be eagerly fetched. The third option also eliminates the need for #JsonIgnore.
(all three options have potentially far-reaching consequences, so you need to decide which one works best for your use case; also note that having to use open-jpa-in-view is a code smell, because forcing the lazy load happens outside of any transactional context)