week 5 junghyunlyoo n 1 - GANGNAM-JAVA/JAVA-STUDY GitHub Wiki

@Entity
@Getter
@NoArgsConstructor
public class Academy {

    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name="academy_id")
    private List<Subject> subjects = new ArrayList<>();

    @Builder
    public Academy(String name, List<Subject> subjects) {
        this.name = name;
        if(subjects != null){
            this.subjects = subjects;
        }
    }

    public void addSubject(Subject subject){
        this.subjects.add(subject);
        subject.updateAcademy(this);
    }
}

@Entity
@Getter
@NoArgsConstructor
public class Subject {

    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "academy_id", foreignKey = @ForeignKey(name = "FK_SUBJECT_ACADEMY"))
    private Academy academy;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "teacher_id", foreignKey = @ForeignKey(name = "FK_SUBJECT_TEACHER"))
    private Teacher teacher;

    @Builder
    public Subject(String name, Academy academy, Teacher teacher) {
        this.name = name;
        this.academy = academy;
        this.teacher = teacher;
    }

    public void updateAcademy(Academy academy){
        this.academy = academy;
    }
}

@Entity
@Getter
@NoArgsConstructor
public class Teacher {

    @Id
    @GeneratedValue
    private Long id;

    private String name;

    public Teacher(String name) {
        this.name = name;
    }
}

@Service
@Slf4j
public class AcademyService {

    private AcademyRepository academyRepository;

    public AcademyService(AcademyRepository academyRepository) {
        this.academyRepository = academyRepository;
    }

    @Transactional(readOnly = true)
    public List<String> findAllSubjectNames(){
        return extractSubjectNames(academyRepository.findAll());
    }

    /**
     * Lazy Load를 수행하기 위해 메소드를 별도로 생성
     */
    private List<String> extractSubjectNames(List<Academy> academies){
        log.info(">>>>>>>>[모든 과목을 추출한다]<<<<<<<<<");
        log.info("Academy Size : {}", academies.size());

        return academies.stream()
                .map(a -> a.getSubjects().get(0).getName())
                .collect(Collectors.toList());
    }
}

@RunWith(SpringRunner.class)
@SpringBootTest
public class AcademyServiceTest {

    @Autowired
    private AcademyRepository academyRepository;

    @Autowired
    private AcademyService academyService;

    @After
    public void cleanAll() {
        academyRepository.deleteAll();
    }

    @Before
    public void setup() {
        List<Academy> academies = new ArrayList<>();

        for(int i=0;i<10;i++){
            Academy academy = Academy.builder()
                    .name("강남스쿨"+i)
                    .build();

            academy.addSubject(Subject.builder().name("자바웹개발" + i).build());
            academies.add(academy);
        }

        academyRepository.save(academies);
    }

    @Test
    public void Academy여러개를_조회시_Subject가_N1_쿼리가발생한다() throws Exception {
        //given
        List<String> subjectNames = academyService.findAllSubjectNames();

        //then
        assertThat(subjectNames.size(), is(10));
    }
}

@Query("select a from Academy a join fetch a.subjects")
List<Academy> findAllJoinFetch();

@Query("select a from Academy a join fetch a.subjects s join fetch s.teacher")
List<Academy> findAllJoinFetch();

@EntityGraph(attributePaths = "subjects")
@Query("select a from Academy a")
List<Academy> findAllEntityGraph();

@EntityGraph(attributePaths = {"subjects", "subjects.teacher"})
@Query("select a from Academy a")
List<Academy> findAllEntityGraph();

@Query("select DISTINCT a from Academy a join fetch a.subjects s join fetch s.teacher")
List<Academy> findAllWithTeacher();

@EntityGraph(attributePaths = {"subjects", "subjects.teacher"})
@Query("select DISTINCT a from Academy a")
List<Academy> findAllEntityGraphWithTeacher();

@OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name="academy_id")
private Set<Subject> subjects = new LinkedHashSet<>();
//LinkedHashSet을 사용하여 순서를 보장