fetch join

• Spring Data JPA 에서 fetch join 이용
• Querydsl 에서 fetch join 이용

• Entity 연관관계 구조
  • BOOK_REVIEW와 USER_INFO가 ManyToOne관계
  • BOOK_REVIEW와 BOOK이 ManyToOne관계

• BOOK을 조회하면 리뷰와 회원 정보가 포함된 결과값을 얻는코드를 작성.
  • BOOK -> BOOK_REVEIW, USER_INFOR

• Sprind Data JPA

@Repository
public interface BookRepository extends CrudRepository<Book, String>, BookRepositoryCustom{

    //ISBN(PK) 으로 도서, 도서에 포함된 리뷰 정보 조회
    @Query(value = "select b from Book b " +
            "join fetch b.bookReviewList br " +
            "join fetch br.userInfo where b.isbn = :isbn")
    Book findByIsbnWithReview(@Param("isbn")String isbn);
}

• Querydsl

public class BookRepositoryImpl implements BookRepositoryCustom{
    private final JPAQueryFactory queryFactory;

    public BookRepositoryImpl(EntityManager entityManager) {
        this.queryFactory = new JPAQueryFactory(entityManager);
    }
    @Override
    public Book findByIsbnWithReview(String isbn) {
        return queryFactory
                .selectFrom(book)
                .join(book.bookReviewList, bookReview).fetchJoin()
                .join(bookReview.userInfo).fetchJoin()
                .where(book.isbn.eq(isbn))
                .fetchOne();
    }

}

• fetch 종류 - 결과 반환 결정
  • fetch : 조회 대상이 여러건일 경우. 컬렉션 반환
  • fetchOne : 조회 대상이 1건일 경우(1건 이상일 경우 에러). generic에 지정한 타입으로 반환
  • fetchFirst : 조회 대상이 1건이든 1건 이상이든 무조건 1건만 반환. 내부에 보면 return limit(1).fetchOne() 으로 되어있음
  • fetchCount : 개수 조회. long 타입 반환
  • fetchResults : 조회한 리스트 + 전체 개수를 포함한 QueryResults 반환. count 쿼리가 추가로 실행된다.

• 결과

select
        book0_.isbn as isbn1_2_0_,
        bookreview1_.review_no as review_n1_3_1_,
        userinfo2_.user_no as user_no1_7_2_,
        book0_.author as author2_2_0_,
        book0_.book_name as book_nam3_2_0_,
        book0_.category as category4_2_0_,
        book0_.contents as contents5_2_0_,
        book0_.book_image as book_ima6_2_0_,
        book0_.kdc as kdc7_2_0_,
        book0_.keyword as keyword8_2_0_,
        book0_.publisher as publishe9_2_0_,
        bookreview1_.isbn as isbn7_3_1_,
        bookreview1_.create_date as create_d2_3_1_,
        bookreview1_.declaration as declarat3_3_1_,
        bookreview1_.rating as rating4_3_1_,
        bookreview1_.review_contents as review_c5_3_1_,
        bookreview1_.review_status as review_s6_3_1_,
        bookreview1_.user_no as user_no8_3_1_,
        bookreview1_.isbn as isbn7_3_0__,
        bookreview1_.review_no as review_n1_3_0__,
        userinfo2_.del_date as del_date2_7_2_,
        userinfo2_.delete_reason as delete_r3_7_2_,
        userinfo2_.last_connection as last_con4_7_2_,
        userinfo2_.user_birth as user_bir5_7_2_,
        userinfo2_.user_gender as user_gen6_7_2_,
        userinfo2_.user_id as user_id7_7_2_,
        userinfo2_.user_name as user_nam8_7_2_,
        userinfo2_.user_priority as user_pri9_7_2_,
        userinfo2_.user_pw as user_pw10_7_2_,
        userinfo2_.user_status as user_st11_7_2_ 
from
        book book0_ 
inner join
        book_review bookreview1_ 
            on book0_.isbn=bookreview1_.isbn 
inner join
	user_info userinfo2_ 
    	on bookreview1_.user_no=userinfo2_.user_no 
where
	book0_.isbn=?