JpaRepository

A ready-made CRUD interface for JPA

Instead of declaring basic operations manually, a JPA repository usually extends JpaRepository. It already contains methods for saving, finding by identifier, checking existence, counting, and deleting entities.

interface CustomerRepository extends JpaRepository<Customer, Long> {
}

@Service
class CustomerService {
    private final CustomerRepository repository;

    CustomerService(CustomerRepository repository) {
        this.repository = repository;
    }

    Customer rename(long id, String name) {
        Customer customer = repository.findById(id).orElseThrow();
        customer.setName(name);
        return repository.save(customer);
    }
}

The interface again has two types: the Customer entity and its Long identifier. After that, methods such as findById, findAll, save, existsById, and deleteById are available.

What save means

save is not a persistence system separate from JPA. For a new entity, Spring Data JPA uses the JPA operation for making it persistent, and for an entity it considers existing, it uses the JPA state-merging mechanism. That is why entity lifecycle and persistence-context rules still matter.