인프런 커뮤니티 질문&답변

MemberRepository

public interface MemberRepository extends JpaRepository<Member, Long> {
    List<Member> findMemberByUsernameAndAgeGreaterThan(String username, int age);

    ...

    @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);
}

MemberRepositoryTest

package hello.datajpa.repository;

...

@SpringBootTest
@Transactional
@Rollback(false)
class MemberRepositoryTest {

    @Autowired MemberRepository memberRepository;
    @Autowired TeamRepository teamRepository;

    ...

    @Test
    public void paging() {
        for (int i = 1; i <= 5; i++) {
            Member member = new Member("member" + i, 10);
            memberRepository.save(member);
        }

        int age = 10;
        PageRequest pageRequest = PageRequest.of(0, 3,
                Sort.by(Sort.Direction.DESC, "username"));
        Page<Member> page = memberRepository.findByAge(age, pageRequest);

        List<Member> content = page.getContent();
        long totalElements = page.getTotalElements();
        int totalPages = page.getTotalPages();
        int currentPage = page.getNumber();
        boolean isFirst = page.isFirst();
        boolean hasNext = page.hasNext();

        assertThat(content.size()).isEqualTo(3);
        assertThat(totalElements).isEqualTo(5);
        assertThat(totalPages).isEqualTo(2);
        assertThat(currentPage).isEqualTo(0);
        assertThat(isFirst).isTrue();
        assertThat(hasNext).isTrue();
    }
}

Member

package hello.datajpa.entity;

...

@Entity
@Getter @Setter
@NoArgsConstructor(access = AccessLevel.PROTECTED)
@ToString(of = {"id", "username", "age"})
/*@NamedQuery(
        name = "Member.findByUsername",
        query = "select m from Member m where m.username = :username"
)*/
public class Member {
    @Id @GeneratedValue
    @Column(name = "member_id")
    private Long id;
    private String username;
    private int age;

    @ManyToOne(fetch = LAZY)
    @JoinColumn(name = "team_id")
    private Team team;

    public Member(String username, int age) {
        this.username = username;
        this.age = age;
    }

    public Member(String username, int age, Team team) {
        this.username = username;
        this.age = age;
        changeTeam(team);
    }

    public void changeTeam(Team team) {
        if (team == null) throw new RuntimeException("Member.changeTeam: team is null");
        this.team = team;
        team.getMembers().add(this);
    }
}

쿼리

select
        m1_0.member_id,
        m1_0.age,
        m1_0.team_id,
        m1_0.username 
    from
        member m1_0 
    order by
        m1_0.username desc offset ? rows fetch first ? rows only




select
        count(m1_0.username) 
    from
        member m1_0

강의와 다르게 left join을 해도 left join 관련 쿼리가 나가지 않는데 뭔가 강의와 다르게 설정된 부분이 있는 걸까요?

@SpringBootTest
@Transactional
@Rollback(false)
class MemberRepositoryTest {

    @Autowired MemberRepository memberRepository;
    @Autowired TeamRepository teamRepository;
    
    ...

    @Test
    public void paging() {
        Team team = new Team("A");
        teamRepository.save(team);

        for (int i = 1; i <= 5; i++) {
            Member member = new Member("member" + i, 10);
            member.changeTeam(team);
            memberRepository.save(member);
        }

        int age = 10;
        PageRequest pageRequest = PageRequest.of(0, 3,
                Sort.by(Sort.Direction.DESC, "username"));
        Page<Member> page = memberRepository.findByAge(age, pageRequest);

        List<Member> content = page.getContent();

        assertThat(team).isSameAs(content.get(0).getTeam()); // team == content.get(0).getTeam() ?

        long totalElements = page.getTotalElements();
        int totalPages = page.getTotalPages();
        int currentPage = page.getNumber();
        boolean isFirst = page.isFirst();
        boolean hasNext = page.hasNext();

        assertThat(content.size()).isEqualTo(3);
        assertThat(totalElements).isEqualTo(5);
        assertThat(totalPages).isEqualTo(2);
        assertThat(currentPage).isEqualTo(0);
        assertThat(isFirst).isTrue();
        assertThat(hasNext).isTrue();
    }
}

테스트 코드를 위와 같이 변경했을 때 left join 쿼리나 select 쿼리가 나가지 않고 assertThat(team).isSameAs(content.get(0).getTeam()) 테스트는 통과됩니다.

위 코드는 이런 식으로 동작하는게 맞을까요?

1. fetch join이 아니기 때문에 하이버네이트는 일단 member만 가져오는 쿼리를 날리고 레코드를 받아온다.

2. 받아온 레코드와 영속성 컨텍스트를 비교한다.

3. 받아온 레코드가 영속성 컨텍스트에 엔티티로 존재하므로 영속성 컨텍스트에 있는 엔티티를 반환한다.

4. 따라서 조회한 content.get(0) 객체에는 team 필드가 이미 할당 되어 있다.