ProgrammingQueryDSL

QueryDSL - 조인

목차

기본 조인

첫 번째 파라미터에 조인 대상을 지정하고, 두번째 파라미터에 별칭으로 사용할 Q 타입을 지정하면 된다.

@Test
public void join(){
    List<Member> result = queryFactory.selectFrom(member)
            .join(member.team, team)
            .where(team.name.eq("teamA"))
            .fetch();

    assertThat(result)
            .extracting("username")
            .containsExactly("member1", "member2");
}
/* select
        member1 
    from
        Member member1   
    inner join
        member1.team as team 
    where
        team.name = ?1 */ select
            member0_.member_id as member_i1_1_,
            member0_.age as age2_1_,
            member0_.team_id as team_id4_1_,
            member0_.username as username3_1_ 
        from
            member member0_ 
        inner join
            team team1_ 
                on member0_.team_id=team1_.team_id 
        where
            team1_.name=?

Seta Join

  • From 절에 여러 엔티티를 선택해서 세타 조인이 가능하다.
  • 외부 조인 불가능
    • 조인 on 을 사용하면 외부 조인 가능
@Test
public void setaJoin(){
    em.persist(new Member("teamA"));
    em.persist(new Member("teamB"));

    List<Member> result = queryFactory.select(member)
            .from(member, team)
            .where(member.username.eq(team.name))
            .fetch();

    assertThat(result)
            .extracting("username")
            .containsExactly("teamA", "teamB");
}
/* select
        member1 
    from
        Member member1,
        Team team 
    where
        member1.username = team.name */ select
            member0_.member_id as member_i1_1_,
            member0_.age as age2_1_,
            member0_.team_id as team_id4_1_,
            member0_.username as username3_1_ 
        from
            member member0_ cross 
        join
            team team1_ 
        where
            member0_.username=team1_.name

ON절을 이용한 JOIN

  • on 절을 활용한 조인
    • 조인 대상 필터링
    • 연관관계 없는 엔티티 외부 조인
@Test
public void join_on_filtering() {
    List<Tuple> result = queryFactory
            .select(member, team)
            .from(member)
            .leftJoin(member.team, team).on(team.name.eq("teamA"))
            .fetch();

    for (Tuple tuple : result) {
        System.out.println("tuple = " + tuple);
    }
}
/* select
        member1,
        team 
    from
        Member member1   
    left join
        member1.team as team with team.name = ?1 */ select
            member0_.member_id as member_i1_1_0_,
            team1_.team_id as team_id1_2_1_,
            member0_.age as age2_1_0_,
            member0_.team_id as team_id4_1_0_,
            member0_.username as username3_1_0_,
            team1_.name as name2_2_1_ 
        from
            member member0_ 
        left outer join
            team team1_ 
                on member0_.team_id=team1_.team_id 
                and (
                    team1_.name=?
                )

연관관계가 없는 엔티티 외부 조인

@Test
public void join_on_no_relation(){
    em.persist(new Member("teamA"));
    em.persist(new Member("teamB"));
    em.persist(new Member("teamB"));

    List<Tuple> fetch = queryFactory
            .select(member, team)
            .from(member)
            .leftJoin(team).on(member.username.eq(team.name))
            .fetch();

    for (Tuple tuple : fetch) {
        System.out.println("tuple = " + tuple);
    }
}
/* select
        member1,
        team 
    from
        Member member1   
    left join
        Team team with member1.username = team.name */ select
            member0_.member_id as member_i1_1_0_,
            team1_.team_id as team_id1_2_1_,
            member0_.age as age2_1_0_,
            member0_.team_id as team_id4_1_0_,
            member0_.username as username3_1_0_,
            team1_.name as name2_2_1_ 
        from
            member member0_ 
        left outer join
            team team1_ 
                on (
                    member0_.username=team1_.name
                )
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