Spring Jpa Entity - EntityManager.getReference

Question

I have a Spring Boot application using Spring JPA, and what I'm trying to do is to save a new entity that has some foreign keys by just providing the IDs of those child entities. So, like:

@Table(name = "PERSON")
public class Person {
@Column(name = "PET_GUID")
public Pet pet;
}

Using this, I'd like to be able to have my PersonRepository that implements CrudRepository save a Person by just providing the guid of the Pet. Using straight up hibernate I can do that using EntityManager.getReference. I know that I can inject an EntityManager into my Entity or Repository and do something that way, but is there an easier way? I tried just doing person.setPet(new Pet(myPetsGuid)), but I get a "foreign key not found" when doing that, so that does not seem to work.

Answer 1

First, you should add @ManyToOne relation to the pet property:

@Entity
@Table(name = "PERSON")
public class Person {

    //...

    @ManyToOne(optional = false, fetch = FetchType.LAZY)
    @JoinColumn(name = "pet_guid")
    privat Pet pet;
}

It says to Hibernate to use a foreign key to the Pet entity (and its table).

Second, you should use the method getOne of your PersonRepository to get a reference to the Pet entity, for example:

@Service
public class PersonService {

    private final PetRepository petRepo;
    private final PersonRepository personRepo;

    //...

    @NonNull
    @Transactional
    public Person create(@NonNull final PersonDto personDto) {
         Person person = new Person();
         //...
         UUID petId = personDto.getPetId();
         Pet pet = petRepo.getOne(perId);
         person.setPet(pet);
         //...
         return person.save(person);
    }

}