Distinction between natural and surrogate identifiers

[martinleim]

Considering the following (synthetic) scenario:
My domain is about managing books. Each book is uniquely identified by a ISBN. Behind the scenes, I want to store the books in a SQL database into an existing schema with an auto-incremented numeric primary key. The callers of that domain should not know nothing about the database, they should only identify books based on the ISBN.

I am now trying to model this with the DDD types. Book looks roughly like this:

public class Book implements AggregateRoot<Book, ISBN> {

    private final ISBN isbn;

    public getId() {
        return isbn;
    }

    public record ISBN(String value) { }
}

I could create a distinct JPA entity which has a numeric @Id, with the isbn as a unique constraint. However, this requires a lot of boilerplate code. I am aware of jmolescules-bytebuddy from the jmolecules-integration. Unfortunately, I cannot use this since it assumes that the identifier of the AggregateRoot is the Id of the JPA entity.

In my opinion, using natural keys (and omitting surrogate ones) in domain models and using auto-incremented primary keys in JPA models are both good practices. Would it be conceivable that jModulecules could support something like this? For instance, there could be an additional annotation to control the JPA boilerplate creation. Tools like jmolescules-bytebuddy could pick that up to create an additional getter with the @Id annotation.

@JpaEntityId(field = "persistenceId")
public class Book implements AggregateRoot<Book, ISBN> {

    private final Integer persistenceId;
    private final ISBN isbn;

    public getId() {
        return getISBN ;
    }

    public getISBN () {
        return isbn;
    }

    // Package-protected visibility, only used within repository
    getPersistenceId() {
        return persistenceId;
    }

    // Package-protected visibility, only used within repository
    Book(Integer persistenceId, ISBN isbn) {
        this.persistenceId = persistenceId;
        this.isbn = isbn;
    }

    public record ISBN(String value) { }
}