Section 7-2. Query By Example

@SpringBootTest
    @Transactional
    public class QueryByExampleTest {
        @Test
        public void basic() throws Exception {
            //given
            Team teamA = new Team("teamA");
            em.persist(teamA);
            em.persist(new Member("m1", 0, teamA));
            em.persist(new Member("m2", 0, teamA));
            em.flush();

            //when
            //Probe 생성
            Member member = new Member("m1");
            Team team = new Team("teamA"); //내부조인으로 teamA 가능
            member.setTeam(team);

            //ExampleMatcher 생성, age 프로퍼티는 무시
            ExampleMatcher matcher = ExampleMatcher.matching().withIgnorePaths("age");
            Example<Member> example = Example.of(member, matcher);
            List<Member> result = memberRepository.findAll(example);

            //then
            assertThat(result.size()).isEqualTo(1);
        }
    }

• Probe: 필드에 데이터가 있는 실제 도메인 객체
• ExampleMatcher: 특정 필드를 일치시키는 상세한 정보 제공, 재사용 가능
• Example: Probe와 ExampleMatcher로 구성, 쿼리를 생성하는데 사용

 

장점

• 동적 쿼리를 편리하게 처리
• 도메인 객체를 그대로 사용
• 데이터 저장소를 RDB에서 NOSQL로 변경해도 코드 변경이 없게 추상화 되어 있음
• 스프링 데이터 JPA JpaRepository 인터페이스에 이미 포함

 

단점

• 조인은 가능하지만 내부 조인(INNER JOIN)만 가능함 외부 조인(LEFT JOIN) 안됨
• 다음과 같은 중첩 제약조건 안됨
  
  • firstname = ?0 or (firstname = ?1 and lastname = ?2)
• 매칭 조건이 매우 단순함
  
  • 문자는 starts/contains/ends/regex
  • 다른 속성은 정확한 매칭( = )만 지원

 

정리

• 실무에서 사용하기에는 매칭 조건이 너무 단순하고, LEFT 조인이 안됨
• 실무에서는 QueryDSL을 사용하자