Spring Data JDBC invert OneToMany navigation

Question

I have an existing data scheme I'm reluctant to change. There are two entities/tables: parent and child, with child having the foreign key column parent_id. It's a 1(parent)-to-n(children) relationship.

Is it possible within Spring Data JDBC to have Child class reference Parent and not Parent have a Set<Child> property? Maybe both? (I know it is possible with hibernate, but I'd like to stay with JDBC).

I.e. I want something like this:

@Data
public class Parent {
    @Id
    private Long id;
}

@Data
public class Child {
    @Id
    private Long id;

    private Parent parent;
}

Somewhat related question: Spring Data JDBC invert OneToOne navigation

Answer 1

Spring Data JDBC doesn't offer direct support for a reference from Child to Parent. If you are modelling Parent and Child as one aggregate, i.e. with a direct reference, Parent must be the aggregate root. So any child gets only accessed the via the Parent at all times. Therefore a back reference should be superfluous.

Actually, the desire to have a back reference might be an indication that the two don't really form a single aggregate but separate aggregates and should be modelled as such. See https://spring.io/blog/2018/09/24/spring-data-jdbc-references-and-aggregates

But if you really want your back reference you can easily establish that in an AfterLoadCallback. For this mark the back reference with the @Transient annotation so it doesn't get actually stored in the database. Then in the AfterLoadCallback which will get triggered once for each Parent navigate from the Parent to each Child and set the back reference.