Hibernate panache same primary key for one to one relations

[haya-hammoud]

Hi
I am using Hibernate ORM with Panache to create my entities, anyone have an idea how to implement OneToOne association that assumes both entities share the same primary key values?

My code looks like this

@Entity
public class Car extends PanacheEntity {

 public String plateNumber;
 public String color;

@OneToOne(optional = true, mappedBy = “car”, cascade = CascadeType.REMOVE, orphanRemoval = true)
    public Ownership ownership;
}

@Entity
public class Onwership extends PanacheEntity {

public String ownerName;

@OneToOne
@MapsId
@JoinColumn(name = "id")
	public Car car;

}

Now, when I’m trying to add ownership (persist) for an existing car, I got this
org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property
I think there is sth wrong with my entities definition. I would appreciate any help.

[quarkus-bot[bot]]

/cc @FroMage, @Sanne, @gsmet, @loicmathieu, @yrodiere

[yrodiere]

Hello,

I'm guessing either Onwership#car or Car#ownership is null?

It would help if you showed the actual code that persists the entities.

[yrodiere]

Ah, actually I didn't see you were using Panache. You'll probably want to extend PanacheEntityBase instead of PanacheEntity when you define your own identifier.

[haya-hammoud]

@yrodiere I can try using PanacheEntityBase but before that can I just ask if it's good practice to do this.
Following illustrations shows two entities that have a OneToOne relation.

• Since a car have one owner and one owner can have only one car, I was thinking that both of these ID's marked in red could be the same. The benefit of doing it this way is that in the resource if I'm querying /owner/{id} or if I'm doing /owner?car={id} , both of the query would give the same result.
• My question is on best practice and if it's the right way to handle OneToOne relation as shown in the diagram - circle 3 colored blue.

My reference:
https://docs.oracle.com/javaee/6/api/javax/persistence/OneToOne.html

 Example 2: One-to-one association that assumes both the source and target share the same primary key values. 

    // On Employee class:

    @Entity
    public class Employee {
        @Id Integer id;
    
        @OneToOne @MapsId
        EmployeeInfo info;
        ...
    }

[yrodiere]

Well that's a lot of trust to put in me, a random stranger on the internet, but okay :) Just keep in mind you can ask the same question to 10 different people and get 10 different answers.

Personally I wouldn't do this unless I have specific reasons, because this complicates your domain model and that can have consequences down the line. For example if you evolve your model and decide that Ownership becomes Owner and an owner can trade his car with another, you'll be in trouble.

One case where it could make sense is if the ID is actually something that has meaning to users, not just some generated integer. But even then you could just use a generated id plus another property annotated with @NaturalId.

Another reason to do it could be performance, maybe. Though I won't try to find an example.

If you neither have a business reason or a performance reason to do this, I'd say don't bother.

I believe @MapsId and similar annotations are mainly there for legacy applications, those that existed before they switched to JPA. If you're designing a new model from scratch... Keep it simple.

[haya-hammoud]

I agree, I think I will just keep it simple by just using a foreign key column
Thanks a lot for the explanation :)