https://medium.com/swlh/jpa-entity-graphs-with-spring-boot-30cb110ba4f8
To define fetching plans programmatically using springboot-starter-data-jpa
N+1 query problem
executes N additional query statements (to fetch the same data that could have been retrieved)
when executing the primary query
primary query : all studies
N additional query: tags, zones, managers, members
Benefits
- Improve the performance when loading entities
- Query all the information from the database at once with JOIN strategy
Basics
Default Entity Graph - Lazy
unless the fetch attribute is set to javax.persistence.FetchType.EAGER
Eager, Lazy
-
attributes that are specified by attribute nodes of the entity graph are treated as FetchType.EAGER
e.g.
@EntityGraph로 정의한 findByPath를 사용하여 조회한 결과는 EAGER 모드가 적용 -
attributes that are not specified are treated as FetchType.LAZY
e.g. 스프링 데이터 JPA가 제공해주는 findByPath
- 경우에 따라서 원하는 방식으로 Fetching 전략을 선택해서 가져올 수 있게 됨
- FETCH: 설정한 엔티티 애트리뷰트는 EAGER 패치 나머지는 LAZY 패치
- LOAD: 설정한 엔티티 애트리뷰트는 EAGER 패치 나머지는 기본 패치 전략 따름
@NamedEntityGraph
override any annotation-based graphs with the same name
Entity
- graph name: Study.withAll
- nodes to be loaded: tags, zones, managers, members
- One Study, N tags, zones, managers, ,members
@NamedEntityGraph(name = "Study.withAll", attributeNodes = {
@NamedAttributeNode("tags"),
@NamedAttributeNode("zones"),
@NamedAttributeNode("managers"),
@NamedAttributeNode("members")})
@NamedEntityGraph(name = "Study.withTagsAndManagers", attributeNodes = {
@NamedAttributeNode("tags"),
@NamedAttributeNode("managers")})
@NamedEntityGraph(name = "Study.withZonesAndManagers", attributeNodes = {
@NamedAttributeNode("zones"),
@NamedAttributeNode("managers")})
@Entity
@Getter @Setter @EqualsAndHashCode(of = "id")
@Builder @AllArgsConstructor @NoArgsConstructor
public class Study {
@Id @GeneratedValue
private Long id;
@ManyToMany
private Set<Tag> tags = new HashSet<>();
@ManyToMany
private Set<Zone> zones = new HashSet<>();
@ManyToMany
private Set<Account> managers = new HashSet<>();
@ManyToMany
private Set<Account> members = new HashSet<>();
}Repository
Declare Interface
depending on the method
@Transactional(readOnly = true)
public interface StudyRepository extends JpaRepository<Study, Long> {
Study findByPath(String path)
@EntityGraph(attributePaths = {"tags", "zones", "managers", "members"},type = EntityGraph.EntityGraphType.LOAD)
Study findByPath(String path);
@EntityGraph(attributePaths = { "tags", "managers" }, type = EntityGraph.EntityGraphType.LOAD)
Study findStudyWithTagsByPath(String path);
@EntityGraph(attributePaths = { "zones", "managers"}, type = EntityGraph.EntityGraphType.LOAD)
Study findStudyWithZonesByPath(String path);
@EntityGraph(attributePaths = "managers")
Study findStudyWithManagersByPath(String path);
@EntityGraph(attributePaths = "members")
Study findStudyWithMembersByPath(String path);
}Service
@Service
public clasee StudyService {
public Study getStudyToUpdateTag(Account account, String path) {
Study study = studyRepository.findStudyWithTagsByPath(path);
checkIfExistingStudy(path, study);
checkIfManager(account, study);
return study;
}
public Study getStudyToUpdateZone(Account account, String path) {
Study study = studyRepository.findStudyWithZonesByPath(path);
checkIfExistingStudy(path, study);
checkIfManager(account, study);
return study;
}
public Study getStudyToUpdateStatus(Account account, String path) {
Study study = studyRepository.findStudyWithManagersByPath(path);
checkIfExistingStudy(path, study);
checkIfManager(account, study);
return study;
}
}Controller
public EventController {
@DeleteMapping("/events/{id}")
public String cancelEvent(@CurrentAccount Account account, @PathVariable String path, @PathVariable Long id) {
Study study = studyService.getStudyToUpdateStatus(account, path);
eventService.deleteEvent(eventRepository.findById(id).orElseThrow());
return "redirect:/study/" + study.getEncodedPath() + "/events";
}
}