[Spring] JPQL(Java Persistence Query Language)

1. JPQL(Java Persistence Query Language) 이란?

(1) 기본 문법

select b from Board b
//b 는 Board 의 모든 데이터를 출력

select b.title,b.content from Board b

select b.title from Board b where b.id = :id;

select b from Board b join fetch b.user u where b.id =:id
//Board 엔티티와 User 엔티티를 조인, Board 엔티티 필트에 User 오브젝트를 넣는다.

2. JPQL 을 활용한 데이터 조회

 select * from board_tb order by id desc;

    public List<Board> findAll(){
        Query query = em.createQuery("select b from Board b order by b.id desc",Board.class);
        return query.getResultList() ;
    }

3. JUnit 테스트

    @Test
    public void findAll_test(){
        //given

        //when
        List<Board> boardList = boardPersistRepository.findAll();
        //then
        System.out.println("findAll_test/size : "+boardList.size());
        System.out.println("findAll_test/username : "+boardList.get(2).getUsername());

        //org.assertj.core.apo
        Assertions.assertThat(boardList.size()).isEqualTo(4);
        Assertions.assertThat(boardList.get(2).getUsername()).isEqualTo("ssar");

    }

4. 컨트롤러

    @GetMapping({ "/"})
    public String index(HttpServletRequest request) {
        List<Board> boardList =  boardPersistRepository.findAll();
        request.setAttribute("boardList",boardList);
        return "index";
    }

5. View 확인하기

    {{#boardList}}
        <div class="card mb-3">
            <div class="card-body">
                <h4 class="card-title">{{title}}</h4>
                <div class="mb-3">{{time}}</div>
                <a href="/board/{{id}}" class="btn btn-primary">상세보기</a>
            </div>
        </div>

    {{/boardList}}