[JPA_Basic] 다대다 매핑

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

 

👉 기본 환경

- Language: Java

- DB: H2 Database

- IDE: IntelliJ

 

 

다대다 매핑

 

import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;
 
@Entity
public class Member {
 
    @Id @GeneratedValue
    @Column(name = "MEMBER_ID")
    private Long id;
 
    @Column(name = "USER_NAME")
    private String name;
 
    @ManyToMany
    @JoinTable(name = "MEMBER_PRODUCT")
    private List<Product> products = new ArrayList<>();
 
}
 

Member Entity

    - 연관 관계 주인

    - JoinTable 생성

 

import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;
 
@Entity
public class Product {
 
    @Id @GeneratedValue
    @Column(name = "PRODUCT_ID")
    private Long id;
 
    @Column(name = "PRODUCT_NAME")
    private String name;
 
    @ManyToMany(mappedBy = "products")
    private List<Member> members = new ArrayList<>();
 
}
 

Product Entity

    - 단순 참조를 위한 매핑

 

⭐ 관계형 데이터베이스에서 다대다 (Many-to-Many) 관계를 직접적으로 표현하는 것은 불가능

    ▶ 연결 테이블을 추가해서 일대다, 다대일 관계로 풀어내야 함

 

⭐ 중간 테이블에 새로운 컬럼을 추가하는 게 어려워 유연성이 떨어짐

    - @JoinTable을 통해서 PK, FK 관계 이외의 필드를 설정하기 어려움

 

Hibernate: 
    
    create table Member (
       MEMBER_ID bigint not null,
        USER_NAME varchar(255),
        primary key (MEMBER_ID)
    )
 
Hibernate: 
    
    create table MEMBER_PRODUCT (
       members_MEMBER_ID bigint not null,
        products_PRODUCT_ID bigint not null
    )
 
Hibernate: 
    
    create table Product (
       PRODUCT_ID bigint not null,
        PRODUCT_NAME varchar(255),
        primary key (PRODUCT_ID)
    )
 
 
Hibernate: 
    
    alter table Member 
       add constraint FK332130jlg9s5hyeuk7gfgi052 
       foreign key (LOCKER_ID) 
       references Locker
 
Hibernate: 
    
    alter table MEMBER_PRODUCT 
       add constraint FKfmfxdrleengm9fi0691plhcwa 
       foreign key (products_PRODUCT_ID) 
       references Product
 
Hibernate: 
    
    alter table MEMBER_PRODUCT 
       add constraint FKp9hlrsu8hrsusdymar0ddcl9o 
       foreign key (members_MEMBER_ID) 
       references Member
 

Entity 실행 결과

 

 

⭐ 다대다 매핑은 일대다 + 다대일 매핑으로 풀어내야 함

 

import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;
 
@Entity
public class Member {
 
    @Id @GeneratedValue
    @Column(name = "MEMBER_ID")
    private Long id;
 
    @Column(name = "USER_NAME")
    private String name;
 
    @OneToMany(mappedBy = "member")
    private List<MemberProduct> memberProducts = new ArrayList<>();
 
}
 

Member Entity

    - Member : MemberProduct = 1: 다

 

import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;
 
@Entity
public class Product {
 
    @Id @GeneratedValue
    @Column(name = "PRODUCT_ID")
    private Long id;
 
    @Column(name = "PRODUCT_NAME")
    private String name;
 
    @OneToMany(mappedBy = "product")
    private List<MemberProduct> memberProducts = new ArrayList<>();
 
}
 

Product Entity

    - Product : MemberProduct = 1: 다

 

import javax.persistence.*;
import java.time.LocalDateTime;
 
@Entity
public class MemberProduct {
 
    @Id @GeneratedValue
    private Long id;
 
    @ManyToOne
    @JoinColumn(name = "PRODUCT_ID")
    private Product product;
 
    @ManyToOne
    @JoinColumn(name = "MEMBER_ID")
    private Member member;
 
    private int count;
    private int price;
 
    private LocalDateTime orderDate;
 
}
 

MemberProduct Entity

    - Member : MemberProduct = 1: 다

    - Product : MemberProduct = 1: 다

 

Hibernate: 
    
    create table Member (
       MEMBER_ID bigint not null,
        USER_NAME varchar(255),
        primary key (MEMBER_ID)
    )
 
Hibernate: 
    
    create table MemberProduct (
       id bigint not null,
        count integer not null,
        orderDate timestamp,
        price integer not null,
        MEMBER_ID bigint,
        PRODUCT_ID bigint,
        primary key (id)
    )
 
Hibernate: 
    
    create table Product (
       PRODUCT_ID bigint not null,
        PRODUCT_NAME varchar(255),
        primary key (PRODUCT_ID)
    )
 
 
Hibernate: 
    
    alter table Member 
       add constraint FK332130jlg9s5hyeuk7gfgi052 
       foreign key (LOCKER_ID) 
       references Locker
 
Hibernate: 
    
    alter table MemberProduct 
       add constraint FKjnj8ungt7v35y6lfxuxcrjbbr 
       foreign key (MEMBER_ID) 
       references Member
 
Hibernate: 
    
    alter table MemberProduct 
       add constraint FKrgt6jorh7iaec1tae84ljye8c 
       foreign key (PRODUCT_ID) 
       references Product
 

Entity 실행 결과