[Spring] 영속성 컨텍스트을 통한 데이터 조회

1. 영속성 객체를 사용한 데이터 조회

    public Board findById(int id) {

        Query query = em.createNativeQuery("select * from board_tb where id =?",Board.class);
        query.setParameter(1,id);
       
         Board board = (Board) query.getSingleResult();
        }

    public Board findById(int id){
        Board board = em.find(Board.class,id);

        return board;
    }

    @Test
    public void fintById_test(){
        int id = 1;
        boardReposiroty.findById(id);
    }

    @Test
    public void fintById_test(){
        int id = 1;
        boardReposiroty.findById(id);
        boardReposiroty.findById(id);  
    }

2. 컨트롤러

    @GetMapping("/board/{id}")
    public String detail(@PathVariable Integer id,HttpServletRequest request) {  // int 를 쓰면 값이 없으면 0, Integer 를 넣으면 값이 없을 때 null 값이 들어옴.

       Board board = boardPersistRepository.findById(id);
        request.setAttribute("board",board);

        return "board/detail";

3. View 확인하기

<div class="container p-5">

    <!-- 수정삭제버튼 -->
    <div class="d-flex justify-content-end">
        <a href="/board/{{board.id}}/update-form" class="btn btn-warning me-1">수정</a>
        <form action="/board/{{board.id}}/delete" method="post">
            <button class="btn btn-danger">삭제</button>
        </form>

    </div>
    <div class="d-flex justify-content-end">
        <b>작성자</b> : {{board.username}}
    </div>

    <!-- 게시글내용 -->
    <div>
        <h2><b>{{board.title}}</b></h2>
        <hr />
        <div class="m-4 p-2">
            {{board.content}}
        </div>
    </div>