Query By Example 간단 예제, 사용

이번 스프링에서 밀어주는 query 탐색법이다. Entity를 생성해서 Example 객체로 변환, repository로 찾아버림
JPA Repository findAll과 같은 메서드에 이미 Example 버전을 만들어 놨다.
(left join이 안되어서 실무에선 주로 QueryDsl을 사용한다.)

버전 1. 그냥 Entity객체 생성해서 실행

 @Test
    public void queryByExampleTest() throws Exception {
        //given
        Team teamA = new Team("teamA");
        Member m1 = new Member("m1",0,teamA);
        Member m2 = new Member("m2",0,teamA);
        em.persist(teamA);
        em.persist(m1);
        em.persist(m2);

        em.flush();
        em.clear();
        //when
        Member targetMem = new Member("m1");//찾고싶은 유저 Entity  
        Example<Member> example = Example.of(targetMem);
        memberRepository.findAll(example);
        //then
    }

    select
        member0_.member_id as member_i1_1_,
        member0_.created_date as created_2_1_,
        member0_.last_modified_date as last_mod3_1_,
        member0_.created_by as created_4_1_,
        member0_.last_modified_by as last_mod5_1_,
        member0_.age as age6_1_,
        member0_.team_id as team_id8_1_,
        member0_.username as username7_1_ 
    from
        member member0_ 
    where
        member0_.age=0 
        and member0_.username=?

버전2. Example Matcher로 조건 걸기

   @Test
    public void queryByExampleTest() throws Exception {
        //given
        Team teamA = new Team("teamA");
        Member m1 = new Member("m1",0,teamA);
        Member m2 = new Member("m2",0,teamA);
        em.persist(teamA);
        em.persist(m1);
        em.persist(m2);

        em.flush();
        em.clear();
        //when
        Member targetMem = new Member("m1");//찾고싶은 유저 Entity


****
        ExampleMatcher matcher = ExampleMatcher.matching()
                .withIgnorePaths("age");//age는 무시하는 matcher 조건 생성 (username만 가져오게 한다)

****        
        Example<Member> example = Example.of(targetMem,matcher);
        memberRepository.findAll(example);
        //then
    }

select
        member0_.member_id as member_i1_1_,
        member0_.created_date as created_2_1_,
        member0_.last_modified_date as last_mod3_1_,
        member0_.created_by as created_4_1_,
        member0_.last_modified_by as last_mod5_1_,
        member0_.age as age6_1_,
        member0_.team_id as team_id8_1_,
        member0_.username as username7_1_ 
    from
        member member0_ 
    where
        member0_.username=? //age가 무시되었다.

Matcher에 다양한 기능이 있다. 공식 spring 문서 참조.

버전3 innerjoin

@Test
    public void queryByExampleTest() throws Exception {
        //given
        Team teamA = new Team("teamA");
        Member m1 = new Member("m1",0,teamA);
        Member m2 = new Member("m2",0,teamA);
        em.persist(teamA);
        em.persist(m1);
        em.persist(m2);

        em.flush();
        em.clear();
        //when
        Member targetMem = new Member("m1");//찾고싶은 유저 Entity
      ***
      Team team = new Team("teamA");
      ***
        targetMem.setTeam(team);


        ExampleMatcher matcher = ExampleMatcher.matching()
                .withIgnorePaths("age");//age는 무시하는 matcher 조건 생성 (username만 가져오게 한다)
        Example<Member> example = Example.of(targetMem,matcher);
        memberRepository.findAll(example);
        //then
    }

 select
        member0_.member_id as member_i1_1_,
        member0_.created_date as created_2_1_,
        member0_.last_modified_date as last_mod3_1_,
        member0_.created_by as created_4_1_,
        member0_.last_modified_by as last_mod5_1_,
        member0_.age as age6_1_,
        member0_.team_id as team_id8_1_,
        member0_.username as username7_1_ 
    from
        member member0_ 
    inner join
        team team1_ 
            on member0_.team_id=team1_.team_id 
    where
        team1_.name=? 
        and member0_.username=?

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장점

• 동적 쿼리를 편리하게 처리
• 도메인 객체를 그대로 사용
• NoSQL로 사용해도 변환 된다.(SpringData쪽 인터페이스를 사용)
• 스프링 데이터 JPA 인터페이스에 이미 포함 JpaRepository

주의사항 💥한계

• inner join까지만 가능하다. left join 등 불가, 아직 부족한 점이 많다. 실무에선 QueryDSL을 사용

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