[JPA_Basic] 조인

이 글은 김영한의 [자바 ORM 표준 JPA 프로그래밍 - 기본편]을 수강하며 정리한 글입니다.

 

👉 기본 환경

- Language: Java

- DB: H2 Database

- IDE: IntelliJ

 

 

Inner Join

⌨️ 코드

public class Main {
    public static void main(String[] args) {
 
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");
 
        EntityManager em = emf.createEntityManager();
 
        EntityTransaction tx = em.getTransaction();
 
        tx.begin(); // transaction 시작 선언
 
        try {
 
            Team team = new Team();
            team.setName("Team");
            em.persist(team);
 
            Member member = new Member();
            member.setName("Member");
            member.setAge(10);
            member.setTeam(team);
            em.persist(member);
 
            em.flush();
            em.clear();
 
            String query = "select m from Member m join m.team t";
 
            List<Member> members = em.createQuery(query, Member.class)
                        .getResultList();
 
            System.out.println("members.size: " + members.size());
            for(Member m : members)
                System.out.println("member: " + m);
 
            tx.commit(); // transaction 종료 후 commit
        } catch (Exception e) {
            tx.rollback(); // 문제가 생길 경우, rollback 진행
            e.printStackTrace();
        } finally {
            em.close(); // tx에 문제가 생기더라도 em 반드시 종료
        }
 
            emf.close();
 
    }
}
 

 

🖨️발생한 쿼리

Hibernate: 
    /* select
        m 
    from
        Member m 
    inner join
        m.team t */ select
            member0_.id as id1_0_,
            member0_.age as age2_0_,
            member0_.name as name3_0_,
            member0_.TEAM_ID as team_id4_0_ 
        from
            Member member0_ 
        inner join
            Team team1_ 
                on member0_.TEAM_ID=team1_.id
 

 

 

Outer Join

⌨️ 코드

public class Main {
    public static void main(String[] args) {
 
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");
 
        EntityManager em = emf.createEntityManager();
 
        EntityTransaction tx = em.getTransaction();
 
        tx.begin(); // transaction 시작 선언
 
        try {
 
            Team team = new Team();
            team.setName("Team");
            em.persist(team);
 
            Member member = new Member();
            member.setName("Member");
            member.setAge(10);
            member.setTeam(team);
            em.persist(member);
 
            em.flush();
            em.clear();
 
            String query = "select m from Member m left join m.team t";
 
            List<Member> members = em.createQuery(query, Member.class)
                        .getResultList();
 
            System.out.println("members.size: " + members.size());
            for(Member m : members)
                System.out.println("member: " + m);
 
            tx.commit(); // transaction 종료 후 commit
        } catch (Exception e) {
            tx.rollback(); // 문제가 생길 경우, rollback 진행
            e.printStackTrace();
        } finally {
            em.close(); // tx에 문제가 생기더라도 em 반드시 종료
        }
 
            emf.close();
 
    }
}
 

 

🖨️발생한 쿼리

Hibernate: 
    /* select
        m 
    from
        Member m 
    left join
        m.team t */ select
            member0_.id as id1_0_,
            member0_.age as age2_0_,
            member0_.name as name3_0_,
            member0_.TEAM_ID as team_id4_0_ 
        from
            Member member0_ 
        left outer join
            Team team1_ 
                on member0_.TEAM_ID=team1_.id
 

 

 

Theta Join

⌨️ 코드

public class Main {
    public static void main(String[] args) {
 
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");
 
        EntityManager em = emf.createEntityManager();
 
        EntityTransaction tx = em.getTransaction();
 
        tx.begin(); // transaction 시작 선언
 
        try {
 
            Team team = new Team();
            team.setName("Team");
            em.persist(team);
 
            Member member = new Member();
            member.setName("Member");
            member.setAge(10);
            member.setTeam(team);
            em.persist(member);
 
            em.flush();
            em.clear();
 
            String query = "select m from Member m, Team t where m.name=t.name";
 
            List<Member> members = em.createQuery(query, Member.class)
                        .getResultList();
 
            System.out.println("members.size: " + members.size());
            for(Member m : members)
                System.out.println("member: " + m);
 
            tx.commit(); // transaction 종료 후 commit
        } catch (Exception e) {
            tx.rollback(); // 문제가 생길 경우, rollback 진행
            e.printStackTrace();
        } finally {
            em.close(); // tx에 문제가 생기더라도 em 반드시 종료
        }
 
            emf.close();
 
    }
}
 

 

🖨️발생한 쿼리

Hibernate: 
    /* select
        m 
    from
        Member m,
        Team t 
    where
        m.name=t.name */ select
            member0_.id as id1_0_,
            member0_.age as age2_0_,
            member0_.name as name3_0_,
            member0_.TEAM_ID as team_id4_0_ 
        from
            Member member0_ cross 
        join
            Team team1_ 
        where
            member0_.name=team1_.name
 

 

 

ON 조건절 활용

1. 조인 대상 필터링

⌨️ 코드

public class Main {
    public static void main(String[] args) {
 
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");
 
        EntityManager em = emf.createEntityManager();
 
        EntityTransaction tx = em.getTransaction();
 
        tx.begin(); // transaction 시작 선언
 
        try {
 
            Team team = new Team();
            team.setName("Team");
            em.persist(team);
 
            Member member = new Member();
            member.setName("Member");
            member.setAge(10);
            member.setTeam(team);
            em.persist(member);
 
            em.flush();
            em.clear();
 
            String query = "select m from Member m join m.team t on t.name= :name";
 
            List<Member> members = em.createQuery(query, Member.class)
                    .setParameter("name", "Team")
                    .getResultList();
 
            System.out.println("members.size: " + members.size());
            for(Member m : members)
                System.out.println("member: " + m);
 
            tx.commit(); // transaction 종료 후 commit
        } catch (Exception e) {
            tx.rollback(); // 문제가 생길 경우, rollback 진행
            e.printStackTrace();
        } finally {
            em.close(); // tx에 문제가 생기더라도 em 반드시 종료
        }
 
            emf.close();
 
    }
}
 

 

🖨️발생한 쿼리

Hibernate: 
    /* select
        m 
    from
        Member m 
    join
        m.team t 
            on t.name= :name */ select
                member0_.id as id1_0_,
                member0_.age as age2_0_,
                member0_.name as name3_0_,
                member0_.TEAM_ID as team_id4_0_ 
        from
            Member member0_ 
        inner join
            Team team1_ 
                on member0_.TEAM_ID=team1_.id 
                and (
                    team1_.name=?
                )
 

⭐ 필터링 후 조인 가능

 

2. 연관관계 없는 엔티티 외부 조인

⌨️ 코드

public class Main {
    public static void main(String[] args) {
 
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");
 
        EntityManager em = emf.createEntityManager();
 
        EntityTransaction tx = em.getTransaction();
 
        tx.begin(); // transaction 시작 선언
 
        try {
 
            Team team = new Team();
            team.setName("Team");
            em.persist(team);
 
            Member member = new Member();
            member.setName("Member");
            member.setAge(10);
            member.setTeam(team);
            em.persist(member);
 
            em.flush();
            em.clear();
 
            String query = "select m from Member m left join m.team t on t.name=m.name";
 
            List<Member> members = em.createQuery(query, Member.class)
                    .getResultList();
 
            System.out.println("members.size: " + members.size());
            for(Member m : members)
                System.out.println("member: " + m);
 
            tx.commit(); // transaction 종료 후 commit
        } catch (Exception e) {
            tx.rollback(); // 문제가 생길 경우, rollback 진행
            e.printStackTrace();
        } finally {
            em.close(); // tx에 문제가 생기더라도 em 반드시 종료
        }
 
            emf.close();
 
    }
}
 

 

🖨️발생한 쿼리

Hibernate: 
    /* select
        m 
    from
        Member m 
    left join
        m.team t 
            on t.name=m.name */ select
                member0_.id as id1_0_,
                member0_.age as age2_0_,
                member0_.name as name3_0_,
                member0_.TEAM_ID as team_id4_0_ 
        from
            Member member0_ 
        left outer join
            Team team1_ 
                on member0_.TEAM_ID=team1_.id 
                and (
                    team1_.name=member0_.name
                )
 

⭐ 연관관계 없이도 외부 조인 가능