페이징과 정렬

• 검색 조건

  • age = 10

• 정렬 조건

  • 이름으로 내림차순

• 페이징 조건

  • 첫 번째 페이지

  • 페이지 당 보여줄 데이터는 3건

순수 JPA

MemberJpaRepository.java

@Repository
public class MemberJpaRepository {

    public List<Member> findByPage(int age, int offset, int limit) {
        return em.createQuery("select m from Member m where m.age = :age order by m.username desc")
                .setParameter("age", age)
                // 어디서 부터 가져올 것인지
                .setFirstResult(offset)
                // 몇 개를 가져올 것인지
                .setMaxResults(limit)
                .getResultList();
    }

    public long totalCount(int age) {
        // 단순 count니까 sort 조건은 빠진다.
        return em.createQuery("select count(m) from Member  m where m.age = :age", Long.class)
                .setParameter("age", age)
                .getSingleResult();
    }
}

MemberJpaRepositoryTest.java

• DB가 달라져도 JPA가 그 DB에 맞는 방언으로 쿼리를 날린다.

스프링 데이터 JPA

파라미터

• org.springframework.data.domain.Sort

  • 정렬

• org.springframework.data.domain.Pageable

  • 페이징

  • 내부에 sort가 포함되어 있다.

반환 타입

interface MemberRepository extends JpaRepository<Member, Long> {
    // count 쿼리 사용
    Page<Member> findByUsername(String name, Pageable pageable);

    // count 쿼리 사용 안함
    Slice<Member> findByUsername(String name, Pageable pageable);

    // count 쿼리 사용 안함
    List<Member> findByUsername(String name, Pageable pageable);

    // count 쿼리 사용 안함
    List<Member> findByUsername(String name, Sort sort);
}

• org.springframework.data.domain.Page

  • 페이징과 total count 쿼리가 같이 나간다.

• org.springframework.data.domain.Slice

  • total count 없이 해당 페이지만 가져온다.

  • 내부적으로 limit + 1만큼 조회한다.

• List

  • total count 쿼리 없이 결과만 반환한다.

예제

Page

MemberRepository.java

public interface MemberRepository extends JpaRepository<Member, Long> {

    Page<Member> findByAge(int age, Pageable pageable);

}

MemberRepositoryTest.java

select member0_.member_id as member_i1_0_,
       member0_.age       as age2_0_,
       member0_.team_id   as team_id4_0_,
       member0_.username  as username3_0_
from member member0_
where member0_.age = 10
order by member0_.username desc limit 3;

select count(member0_.member_id) as col_0_0_
from member member0_
where member0_.age = 10;

• count를 구하는 별도의 메서드 없이 자동으로 날린다.

• PageRequest

  • Pageable 인터페이스를 구현한 객체

Slice

MemberRepository.java

public interface MemberRepository extends JpaRepository<Member, Long> {

    Slice<Member> findByAge(int age, Pageable pageable);

}

MemberRepositoryTest.java

select member0_.member_id as member_i1_0_,
       member0_.age       as age2_0_,
       member0_.team_id   as team_id4_0_,
       member0_.username  as username3_0_
from member member0_
where member0_.age = 10
order by member0_.username desc limit 4;

• count를 가져오지 않는다.

• 컨텐츠만 limit + 1만큼 가져온다.

• 더보기 방식으로 개발할 때 사용한다.

List

MemberRepository.java

public interface MemberRepository extends JpaRepository<Member, Long> {

    List<Member> findByAge(int age, Pageable pageable);

}

MemberRepositoryTest.java

select member0_.member_id as member_i1_0_,
       member0_.age       as age2_0_,
       member0_.team_id   as team_id4_0_,
       member0_.username  as username3_0_
from member member0_
where member0_.age = 10
order by member0_.username desc limit 3;

Count 최적화

public interface MemberRepository extends JpaRepository<Member, Long> {

    @Query(value = "select m from Member m left join m.team t")
    Page<Member> findByAge(int age, Pageable pageable);

}

select member0_.member_id as member_i1_0_,
       member0_.age       as age2_0_,
       member0_.team_id   as team_id4_0_,
       member0_.username  as username3_0_
from member member0_
         left outer join team team1_ on member0_.team_id = team1_.team_id
order by member0_.username desc limit 3;

select count(member0_.member_id) as col_0_0_
from member member0_
         left outer join team team1_ on member0_.team_id = team1_.team_id;

• count 쿼리는 매번 총 개수를 세야 해서 부하가 생긴다.

• join으로 가져오는 데이터라면 count 쿼리에 불필요한 join이 나간다.

public interface MemberRepository extends JpaRepository<Member, Long> {

    @Query(value = "select m from Member m left join m.team t", countQuery = "select count(m.username) from Member m")
    Page<Member> findByAge(int age, Pageable pageable);

}

select member0_.member_id as member_i1_0_,
       member0_.age       as age2_0_,
       member0_.team_id   as team_id4_0_,
       member0_.username  as username3_0_
from member member0_
         left outer join team team1_ on member0_.team_id = team1_.team_id
order by member0_.username desc limit 3;

select count(member0_.username) as col_0_0_
from member member0_;

• countQuery를 사용하면 count 쿼리가 심플하게 나간다.

페이지를 유지하면서 엔티티를 DTO로 변환

@SpringBootTest
@Transactional
@Rollback(value = false)
class MemberRepositoryTest {
    @Test
    void paging() {
        
        ...

        Page<Member> page = memberRepository.findByAge(10, pageRequest);
        Page<MemberDto> dtoPage = page.map(m -> new MemberDto(m.getId(), m.getUsername()));

      ...
    }
}

• map

  • 엔티티 그대로 컨트롤러에서 넘기면 안되므로 DTO로 변환한다.