[JPA] 같은 트랜잭션안에서는 영속성 컨택스트의 동일성을 보장함

@Transactional

@SpringBootTest
@Rollback(value = false)
class MemberJpaRepositoryTest {
    @Autowired
    MemberJpaRepository memberJpaRepository;
    @Test
    public void testMember(){
        Member member = new Member("memberA");
        Member savedMember = memberJpaRepository.save(member);

        Member findMember = memberJpaRepository.find(savedMember.getId());

        assertThat(findMember.getId()).isEqualTo(member.getId());
        assertThat(findMember.getUserName()).isEqualTo(member.getUserName());

    }
}

022-09-24 15:57:01.005 DEBUG 13116 --- [           main] org.hibernate.SQL                        : 
    insert 
    into
        member
        (user_name, id) 
    values
        (?, ?)
2022-09-24 15:57:01.013  INFO 13116 --- [           main] o.s.t.c.transaction.TransactionContext   : Committed transaction for test: [DefaultTestContext@2f4205be testClass = MemberJpaRepositoryTest, testInstance = stduy.datajpa.repository.MemberJpaRepositoryTest@20f6b6e0, testMethod = testMember@MemberJpaRepositoryTest, testException = [null], mergedContextConfiguration = [WebMergedContextConfiguration@54e22bdd testClass = MemberJpaRepositoryTest, locations = '{}', classes = '{class stduy.datajpa.DataJpaApplication}', contextInitializerClasses = '[]', activeProfiles = '{}', propertySourceLocations = '{}', propertySourceProperties = '{org.springframework.boot.test.context.SpringBootTestContextBootstrapper=true}', contextCustomizers = set[org.springframework.boot.test.autoconfigure.actuate.metrics.MetricsExportContextCustomizerFactory$DisableMetricExportContextCustomizer@7ac296f6, org.springframework.boot.test.autoconfigure.properties.PropertyMappingContextCustomizer@0, org.springframework.boot.test.autoconfigure.web.servlet.WebDriverContextCustomizerFactory$Customizer@18ece7f4, org.springframework.boot.test.context.filter.ExcludeFilterContextCustomizer@264f218, org.springframework.boot.test.json.DuplicateJsonObjectContextCustomizerFactory$DuplicateJsonObjectContextCustomizer@81d9a72, org.springframework.boot.test.mock.mockito.MockitoContextCustomizer@0, org.springframework.boot.test.web.client.TestRestTemplateContextCustomizer@1e13529a, org.springframework.boot.test.context.SpringBootTestArgs@1, org.springframework.boot.test.context.SpringBootTestWebEnvironment@5e25a92e], resourceBasePath = 'src/main/webapp', contextLoader = 'org.springframework.boot.test.context.SpringBootContextLoader', parent = [null]], attributes = map['org.springframework.test.context.web.ServletTestExecutionListener.activateListener' -> true, 'org.springframework.test.context.web.ServletTestExecutionListener.populatedRequestContextHolder' -> true, 'org.springframework.test.context.web.ServletTestExecutionListener.resetRequestContextHolder' -> true, 'org.springframework.test.context.event.ApplicationEventsTestExecutionListener.recordApplicationEvents' -> false]]
2022-09-24 15:57:01.037  INFO 13116 --- [ionShutdownHook] j.LocalContainerEntityManagerFactoryBean : Closing JPA EntityManagerFactory for persistence unit 'default'
2022-09-24 15:57:01.040  INFO 13116 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
2022-09-24 15:57:01.064  INFO 13116 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.

Process finished with exit code 0

savedMember와 findMember는 같은 트랜잭션이기 때문에 동일성을 보장해준다.

savedMember가 em.persist로 1차 캐시에 저장되고

findMember가 1차캐시를 먼저 찾아보고 savedMember를 가지고 오기 때문에 findMember를 찾기위한 select문이 나가지않았다.