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insert into room
        (detailed_address, lot_address, post_code, road_address, capacity, description, host_id, name, price_per_day) 
    values
        (?, ?, ?, ?, ?, ?, ?, ?, ?)

insert into room_photo
        (file_name) 
    values
        (?)
insert into room_photo
        (file_name) 
    values
        (?)

update room_photo 
    set
        room_id=? 
    where
        id=?

update room_photo 
    set
        room_id=? 
    where
        id=?

마찬가지로 삭제 시에도, RoomPhoto 테이블에서 FK를 null 처리 해주는 update 쿼리 이후에 roomPhoto삭제, room 삭제를 실행함


Member member1 = new Member("member1");
Member member2 = new Member("member2");

Team team1 = new Team("team1");
team1.getMembers().add(member1);
team1.getMembers().add(member2);

em.persist(member1); // INSERT-member1
em.persist(member2); // INSERT-member2
em.persist(team1); // INSERT-team1, UPDATE-member1.fk, UPDATE-member2.fk

transcation.commit();

Member는 Team을 모르기에 Member 엔티티를 저장할 때는 MEMBER 테이블의 TEAM_ID가 null. 그 후 Team 엔티티를 저장할 때 Team.members의 참조 값을 확인해서 회원 테이블에 있는 TEAM_ID 외래 키를 업데이트 함


public class Team{
	@OneToMany(cascade=ALL)
	@JoinColumn("team_id")
	private List<Member> members = new ArrayList<>();
}

public class Member{
}

Member member1 = new Member("member1");
Member member2 = new Member("member2");

Team team1 = new Team("team1");
team1.getMembers().add(member1);
team1.getMembers().add(member2);

em.persist(team1); // INSERT-team1, insert member1, insert member2
// UPDATE-member1.fk, UPDATE-member2.fk

transcation.commit();


public class Team{
	@OneToMany(cascade=ALL, mappedBy = "team") // mappedBy는 필드이름
	private List<Member> members = new ArrayList<>();
}

public class Member{

	@ManyToOne(fetch = FetchType.LAZY, optional = false)
	@JoinColumn(name="team_id") // db에서 관리할 컬럼이름
	private Team team;
}

Member member1 = new Member("member1");
Member member2 = new Member("member2");

Team team1 = new Team("team1");
team1.getMembers().add(member1);
team1.getMembers().add(member2);
member1.setTeam(team1); // 얘네가 연관관계의 주인이기에, 연관관계 설정 해주어야 함
member2.setTeam(team2); // 연관관계 설정 안하고 cascade만 하면 데이터는 들어가는데
// FK(team_id) 가 null임

em.persist(team1); // INSERT-team1, insert member1, insert member2
// UPDATE-member1.fk, UPDATE-member2.fk

transcation.commit();

@OneToMany 단방향 문제점

근데, 양방향으로 할 시, 연관관계의 주인에서 연관관계 세팅을 해주어야 한다는 귀찮음이 있음!