JPA 객체지향 쿼리 언어(JPQL) - 엔티티 직접 사용

출처 : 자바 ORM 표준 JPA 프로그래밍 인프런 강의

 

JPA 게시글은 대부분 인프런의 김영한님의 강의인 '자바 ORM 표준 JPA 프로그래밍' 기반으로 내용을 정리했습니다.

 

엔티티 직접 사용

기본 키 값

• JPQL에서 엔티티를 직접 사용하면 SQL에서 해당 엔티티의 기본 키 값을 사용
• JPQL

select count(m.id) from Member m // 엔티티의 아이디를 사용
select count(m) from Member m // 엔티티를 직접 사용

• SQL(JPQL 둘 다 다음과 같은 SQL 실행)

select count(m.id) as cnt from Member m

• 엔티티를 파라미터로 전달

String query = "select m From Member m where m = :member";
Member findMember = em.createQuery(query, Member.class)
        .setParameter("member", member)
        .getSingleResult();

• 식별자를 직접 전달

String query = "select m From Member m where m.id = :memberId";
Member findMember = em.createQuery(query, Member.class)
        .setParameter("memberId", member.getId())
        .getSingleResult();

• 실행된 SQL

Hibernate: 
    /* select
        m 
    From
        Member m 
    where
        m.id = :memberId */ select
            member0_.id as id1_0_,
            member0_.age as age2_0_,
            member0_.TEAM_ID as TEAM_ID5_0_,
            member0_.type as type3_0_,
            member0_.username as username4_0_ 
        from
            Member member0_ 
        where
            member0_.id=?

 

 

외래 키 값

String query = "select m From Member m where m.team = :team"; // m.team이 DB 입장에서는 외래키
List<Member> findMember = em.createQuery(query, Member.class)
        .setParameter("team", teamA)
        .getResultList();

for (Member mem : findMember) {
    System.out.println("mem = " + mem);
}

Hibernate: 
    /* select
        m 
    From
        Member m 
    where
        m.team = :team */ select
            member0_.id as id1_0_,
            member0_.age as age2_0_,
            member0_.TEAM_ID as TEAM_ID5_0_,
            member0_.type as type3_0_,
            member0_.username as username4_0_ 
        from
            Member member0_ 
        where
            member0_.TEAM_ID=?
mem = Member{id=3, username='회원1', age=0}
mem = Member{id=4, username='회원2', age=0}