How to work with @CreatedBy in Spring?

Question

Java

Good day (although it's already night) I
use Auditing. The domain has:

@ManyToOne
@JoinColumn
@CreatedBy
private User user;

The User object is valid. But not persistent, as a result of which, when trying to write to the database, a sheet falls out, motivated by the fact that object references an unsaved transient instance.
I understand it, but nevertheless, where should I save the transient instance (and how, is it really possible to load the UserRepo) when it is written just with @PrePersist?
How to solve this problem?
P. S On the Internet they write about CascadeType.ALL, but that's not it, because my User does not depend on the domain

Answer 1

I found a solution.
The fact is that I getCurrentUser()returned the newly created User object, but I had to pull it from the database using the repo (so that the object would immediately be persisted, not detached).
Mine getCurrentUser()now:

@Override
    public Optional<User> getCurrentAuditor() {
        Authentication auth = SecurityContextHolder.getContext().getAuthentication();
        UserDetails userDetails = (UserDetails) auth.getPrincipal();
        return this.userRepository.findByLogin(userDetails.getUsername());
    }

Answer 2

You need to write a component that will return you the current logged in user from the context.
To do this, you need to create a new component that implements the AuditorAware interface.
More or less like this:

@Component
public class UserAuditorAware implements AuditorAware<User> {
    @Override
    public Optional<User> getCurrentAuditor() {
        SecurityContext context = SecurityContextHolder.getContext();
        // из контекста получаете userId или его имя, смотря что там храните.
        Long userId = //;
        return Optional.of(new User(userId));
    }
}

also, don't forget to make columns for createBy or createAt non-editable.