@Transacional의 범위에 대해서 궁금한 점이 하나 있습니다!

안녕하세요 강사님. 항상 훌륭한 강의 감사드립니다.

스프링 MVC 1, 2편에서 사용했던 프로젝트에 JPA를 적용시키는 도중 궁금한점이 하나 생겨서 질문드립니다.

TestInitData 클래스에 @PostConstruct로 데이터베이스에 초기 데이터들을 넣어두려고 합니다.

package com.myservice.web.test;

import com.myservice.domain.item.Item;
import com.myservice.domain.item.ItemRepository;
import com.myservice.domain.member.Grade;
import com.myservice.domain.member.Member;
import com.myservice.domain.member.MemberRepository;
import com.myservice.domain.member.MemberService;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
import org.springframework.transaction.annotation.Transactional;

import javax.annotation.PostConstruct;

@Slf4j
@Component
@RequiredArgsConstructor
@Transactional
public class TestDataInit {

    private final ItemRepository itemRepository;
    private final MemberService memberService;
    private final MemberRepository memberRepository;

    /**
     * 테스트용 데이터 추가
     */
    @PostConstruct
    public void init() {
        itemRepository.save(new Item("itemA", 10000, 10));
        itemRepository.save(new Item("itemB", 20000, 20));
        itemRepository.save(new Item("itemC", 15000, 15));

        Member member1 = new Member();
        member1.setLoginId("manager");
        member1.setPassword("manager");
        member1.setUsername("최한슬");
        member1.setGrade(Grade.MANAGER);

        Member member2 = new Member();
        member2.setLoginId("user");
        member2.setPassword("user");
        member2.setUsername("USER");

        //바로 memberRepository.save로 접근하면 현재 스레드에서 사용할 수 있는 EntityManager가 없다고 오류 발생
        memberRepository.save(member1);
        memberRepository.save(member2);
        //memberService.save -> memberRepository.save로 접근하면 정상적으로 작동
        memberService.save(member1);
        memberService.save(member2);
    }

}

또한, memberRepository와 memberService는 다음과 같습니다.

[memberRepository]

package com.myservice.domain.member;

import org.springframework.stereotype.Repository;

import java.util.List;
import java.util.Optional;

@Repository
public interface MemberRepository {

    Long save(Member member);

    Optional<Member> findById(Long id);

    Optional<Member> findByLoginId(String loginId);

    List<Member> findAll();
}

package com.myservice.domain.member;

import lombok.RequiredArgsConstructor;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Repository;

import javax.persistence.EntityManager;
import java.util.List;
import java.util.Optional;

@Repository
@RequiredArgsConstructor
@Primary
public class JpaMemberRepository implements MemberRepository {

    private final EntityManager em;

    @Override
    public Long save(Member member) {
        em.persist(member);
        return member.getId();
    }

    @Override
    public Optional<Member> findById(Long id) {
        Member member = em.find(Member.class, id);
        return Optional.ofNullable(member);
    }

    @Override
    public Optional<Member> findByLoginId(String loginId) {
        Member member = em.createQuery("select m from Member m where m.loginId = :loginId", Member.class)
                .setParameter("loginId", loginId)
                .getResultStream()
                .findAny()
                .orElse(null);

        return Optional.ofNullable(member);
    }

    @Override
    public List<Member> findAll() {
        return em.createQuery("select m from Member m", Member.class)
                .getResultList();
    }

}

[memberService]

package com.myservice.domain.member;

import lombok.RequiredArgsConstructor;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
@Transactional
@RequiredArgsConstructor
public class MemberService {

    private final MemberRepository memberRepository;

    public void save(Member member) {
        memberRepository.save(member);
    }
}

현재 MemberService에는 @Transactional이 걸려있고, memberRepository에는 @Transactional 걸려있지 않습니다.

궁금한점은 TestDataInit 클래스의 init() 메서드에서 바로 memberRepository로 접근하게되면 사용할 수 있는 EntityManager가 없다고 나오며,

memberService->memberRepository로 접근하게 되면 정상적으로 처리되는 것을 확인하였습니다.

두 방식 모두 결국 memberRepository를 통해 save를 수행하게 되는데 바로 memberRepository의 접근은 오류가 발생하고 memberService를 통한 접근은 정상적으로 처리되는 이유를 모르겠습니다.