[ JPA ] 5-2. Entity Relations ( 1:1 @OneToOne )

Reference. 한 번에 끝내는 Java/Spring 웹 개발 마스터 초격차 패키지 Online

이전 글

1. Repository interface 메서드

2. Query Method 정의 및 실습

3. Entity 기본 속성

4. Entity Listener

5-1. Entity Relations (ERD, 데이터베이스 기준 연관 관계)

1. 속성

• @OneToOne 속성
  • optional: 데이터가 필수적(not null)인지, 아닌지(null) 여부 ( default: true )
    → 필수적일 때(optional = false) 컬럼은 not null, select 쿼리는 inner join으로 변경

    Hibernate: 
        
        create table book_review_info (
           id bigint generated by default as identity,
            created_at timestamp,
            updated_at timestamp,
            average_review_score float not null,
            review_count integer not null,
            book_id bigint not null,
            primary key (id)
        )
    
    Hibernate: 
        select
            bookreview0_.id as id1_2_0_,
            bookreview0_.created_at as created_2_2_0_,
            bookreview0_.updated_at as updated_3_2_0_,
            bookreview0_.average_review_score as average_4_2_0_,
            bookreview0_.book_id as book_id6_2_0_,
            bookreview0_.review_count as review_c5_2_0_,
            book1_.id as id1_1_1_,
            book1_.created_at as created_2_1_1_,
            book1_.updated_at as updated_3_1_1_,
            book1_.author_id as author_i4_1_1_,
            book1_.category as category5_1_1_,
            book1_.name as name6_1_1_,
            book1_.publisher_id as publishe7_1_1_ 
        from
            book_review_info bookreview0_ 
        inner join
            book book1_ 
                on bookreview0_.book_id=book1_.id 
        where
            bookreview0_.id=

  • mappedBy: 연관키를 해당 테이블에서는 가지지 않음
    • mappedBy="bookReviewInfo" 해당 Entity의 bean id로 사용, 값이 안맞으면 에러

    //mappedBy 설정 전
    public class BookReviewInfo extends BaseEntity{
    		...
    		@OneToOne(optional = false)
        private Book book;	
    		...
    }
    
    //실행결과 DDL book_id bigint not null
    Hibernate: 
        
    create table book_review_info (
       id bigint generated by default as identity,
        created_at timestamp,
        updated_at timestamp,
        average_review_score float not null,
        review_count integer not null,
        book_id bigint not null,
        primary key (id)
    )

    //mappedBy 설정 후
    public class BookReviewInfo extends BaseEntity{
    		...
    		@OneToOne(optional = false, mappedBy = "bookReviewInfo")
        private Book book;	
    		...
    }
    
    //실행결과 DDL book_id 없어짐
    Hibernate: 
    
        create table book_review_info (
           id bigint generated by default as identity,
            created_at timestamp,
            updated_at timestamp,
            average_review_score float not null,
            review_count integer not null,
            primary key (id)
        )

2. 최종 실행

• @ToString.Exclude: Entity 릴레이션을 사용하는 경우에 toString()가 순환참조가 발생. 릴레이션을 단방향으로 걸거나 toString()에서 제거 필요 ( @ToString.exclude )

Book.java

public class Book extends BaseEntity{
		...
		@OneToOne(mappedBy = "book")
    @ToString.Exclude
    private BookReviewInfo bookReviewInfo;
}

BookReviewInfo.java

public class BookReviewInfo extends BaseEntity{
		...
		@OneToOne(optional = false)
    private Book book;	
		...
}

실행결과

//book에서 book_review_info_id가 mappedBy의해 사라짐
Hibernate: 
    
    create table book (
       id bigint generated by default as identity,
        created_at timestamp,
        updated_at timestamp,
        author_id bigint,
        category varchar(255),
        name varchar(255),
        publisher_id bigint,
        primary key (id)
    )

Hibernate: 
    
    create table book_review_info (
       id bigint generated by default as identity,
        created_at timestamp,
        updated_at timestamp,
        average_review_score float not null,
        review_count integer not null,
        book_id bigint not null,
        primary key (id)
    )

//쿼리 로그
Hibernate: 
    select
        bookreview0_.id as id1_2_0_,
        bookreview0_.created_at as created_2_2_0_,
        bookreview0_.updated_at as updated_3_2_0_,
        bookreview0_.average_review_score as average_4_2_0_,
        bookreview0_.book_id as book_id6_2_0_,
        bookreview0_.review_count as review_c5_2_0_,
        book1_.id as id1_1_1_,
        book1_.created_at as created_2_1_1_,
        book1_.updated_at as updated_3_1_1_,
        book1_.author_id as author_i4_1_1_,
        book1_.category as category5_1_1_,
        book1_.name as name6_1_1_,
        book1_.publisher_id as publishe7_1_1_ 
    from
        book_review_info bookreview0_ 
    inner join
        book book1_ 
            on bookreview0_.book_id=book1_.id 
    where
        bookreview0_.id=?

>>>Book(super=BaseEntity(createdAt=2021-07-25T10:06:09.851706, updatedAt=2021-07-25T10:06:09.851706), id=1, name=JPA 책, category=null, authorId=1, publisherId=1)

Hibernate: 
    select
        book0_.id as id1_1_0_,
        book0_.created_at as created_2_1_0_,
        book0_.updated_at as updated_3_1_0_,
        book0_.author_id as author_i4_1_0_,
        book0_.category as category5_1_0_,
        book0_.name as name6_1_0_,
        book0_.publisher_id as publishe7_1_0_,
        bookreview1_.id as id1_2_1_,
        bookreview1_.created_at as created_2_2_1_,
        bookreview1_.updated_at as updated_3_2_1_,
        bookreview1_.average_review_score as average_4_2_1_,
        bookreview1_.book_id as book_id6_2_1_,
        bookreview1_.review_count as review_c5_2_1_ 
    from
        book book0_ 
    left outer join
        book_review_info bookreview1_ 
            on book0_.id=bookreview1_.book_id 
    where
        book0_.id=?

>>>BookReviewInfo(super=BaseEntity(createdAt=2021-07-25T10:06:09.953707, updatedAt=2021-07-25T10:06:09.953707), id=1, book=Book(super=BaseEntity(createdAt=2021-07-25T10:06:09.851706, updatedAt=2021-07-25T10:06:09.851706), id=1, name=JPA 책, category=null, authorId=1, publisherId=1), averageReviewScore=4.5, reviewCount=2)