@Entity
@Table(name = "documents")
public class Document implements Comparable<Document> {

    @Id
    @Column(name = "document_id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long documentId;

    @OneToOne(mappedBy = "document", cascade = CascadeType.ALL, optional = false, fetch = FetchType.LAZY)
    private DocumentTmp documentTmp;
}

@Entity
@Table(name = "document_tmp")
public class DocumentTmpEntity {
    @Id
    @Column(name = "document_content_tmp_id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long documentContentTmpId;

    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "document_id", nullable = false)
    private Document document;
}

@Repository
public interface DocumentTmpRepository extends CrudRepository<DocumentTmpEntity, Long> {}

@Transactional
public Document getDocument(){
    Iterable<DocumentTmpEntity> documentTmpList = documentTmpRepository.findAll();
    for (DocumentTmpEntity documentTmp : documentTmpList) {
        Document document = documentTmp.getDocument();
    }
}

@Query(value = "select d from DocumentTmpEntity d join fetch d.document")
List<DocumentTmpEntity> lazyLoad();