[JPQL] 엔티티 직접 사용

1. 엔티티 직접 사용 - 기본 키 값

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• JPQL에서 엔티티를 직접 사용하면 SQL에서 해당 엔티티의 기본 키 값을 사용함!
• 엔티티는 DB에서 구분되는 기준이 기본 키임. 따라서 엔티티를 넘겨도 PK를 사용함.
• JPQL

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

• SQL : 위 JPQL 둘다 아래와 같이 동일한  SQL 실행.

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

• 엔티티를 파라미터로 전달하는 경우

  • String jpql = “select m from Member m where m = :member”; 
    List resultList = em.createQuery(jpql) 
     .setParameter("member", member) 
     .getResultList();

  •  
  • Hibernate: /* select m from Member m where m = :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=?
• 식별자를 전달하는 경우

  • String jpql = “select m from Member m where m.id = :memberId”; 
    List resultList = em.createQuery(jpql) 
     .setParameter("memberId", memberId) 
     .getResultList();

  • 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=?

• 실행된 SQL

  • select m.* from Member m where m.id=?

 

 

 

2. 엔티티 직접 사용 - 외래 키 값.

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• 엔티티로 넘기는 경우

Team team = em.find(Team.class, 1L); 
String qlString = “select m from Member m where m.team = :team”; 
List resultList = em.createQuery(qlString) 
 .setParameter("team", team) 
 .getResultList();

• 식별자(FK) 로 넘기는 경우

String qlString = “select m from Member m where m.team.id = :teamId”; 
List resultList = em.createQuery(qlString) 
 .setParameter("teamId", teamId) 
 .getResultList();

• 실행된 SQL : FK사용함(연관된 FK 사용)

select m.* from Member m where m.team_id=?