[스프링부트 blogV2] 2.Repository - jpql로 작성하기, Optional을 이용한 null처리

  public List<Board> findAll() {
    return em.createQuery("select b from Board b order by b.id").getResultList();
  }

  public Optional<Board> findById(int id) {

    return Optional.ofNullable(em.find(Board.class, id));
  }

  public void save(Board board) {  // board 객체를 만들어서 던지면 insert해준다.
    em.persist(board);
  }

  public void delete(int id) {
    em.createQuery("delete from Board b where b.id = :id").setParameter("id", id).executeUpdate();
  }

  public Optional<Board> findById(int id) {
   
    return Optional.ofNullable(em.find(Board.class, id));
  }

Service

  public BoardResponse.DetailDTO 게시글상세보기(int id) {
    Board board = boardRepository.findById(id)
        .orElseThrow(()->new RuntimeException("해당 id의 게시글이 없습니다:"+id));
    return new BoardResponse.DetailDTO(board);
  }