[자바 ORM 표준 JPA] ch6.다양한 연관관계 매핑 - 다대다
다대다
DB에선 테이블 두개만으로 표현 할 수 없습니다.
그래서 중간에 관계 테이블을 추가합니다.
객체지향에선 객체 2개로 다대다 관계를 만들 수 있습니다.
➡️ 단방향
@JoinTable 의 속성
- @JoinTable.name : 연결 테이블의 이름입니다. 코드상으로는
member_product가 됩니다. - @JoinTable.joinColumns :
@JoinTable을 사용한Member에서 조인에 사용할 컬럼입니다. - @JoinTable.inverseJoinColumns :
@JoinTable을 사용하지 않은Product에서 조인에 사용할 컬럼입니다.
@Entity
@NoArgsConstructor
public class Member {
@Id @GeneratedValue
@Column(name = "MEMBER_ID")
private Long id;
private String username;
@ManyToMany
@JoinTable(name = "MEMBER_PRODUCT",
joinColumns = @JoinColumn(name = "MEMBER_ID"),
inverseJoinColumns = @JoinColumn(name = "PRODUCT_ID"))
private List<Product> products = new ArrayList<Product>();
}
@Entity
@NoArgsConstructor
public class Product {
@Id @GeneratedValue
@Column(name = "PRODUCT_ID")
private Long id;
private String name;
}
코드 설명
@ManyToMany는 기본적으로 지연로딩입니다. 따라서Member를 조회할 땐 Join이 발생하지 않고Product를 사용하려는 순간 조인이 발생 됩니다.- 트랜잭션 커밋후 1차 캐시를 비우지 않고 조회하면 1차 캐시에 있는 데이터를 조회하므로 Select 쿼리가 날아가지 않게 됩니다.
public class _1_Test {
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("myApp");
EntityManager em = emf.createEntityManager();
EntityTransaction tx = em.getTransaction();
tx.begin();
Product note = new Product();
note.setName("note");
Product pen = new Product();
pen.setName("pen");
em.persist(note);
em.persist(pen);
Member member = new Member();
member.setUsername("cho");
member.getProducts().add(note);
member.getProducts().add(pen);
em.persist(member);
tx.commit();
em.clear();
Member cho = em.find(Member.class, member.getId());
System.out.println("----- " + cho.getUsername() + " 회원님의 주문상품 목록 -----");
cho.getProducts().forEach(product -> {
System.out.println("product = " + product.getName());
});
emf.close();
}
}
-
JPA LOG
Hibernate: select nextval ('hibernate_sequence') Hibernate: select nextval ('hibernate_sequence') Hibernate: select nextval ('hibernate_sequence') Hibernate: insert into Product (name, PRODUCT_ID) values (?, ?) Hibernate: insert into Product (name, PRODUCT_ID) values (?, ?) Hibernate: insert into Member (username, MEMBER_ID) values (?, ?) Hibernate: insert into MEMBER_PRODUCT (MEMBER_ID, PRODUCT_ID) values (?, ?) Hibernate: insert into MEMBER_PRODUCT (MEMBER_ID, PRODUCT_ID) values (?, ?) Hibernate: select member0_.MEMBER_ID as member_i1_0_0_, member0_.username as username2_0_0_ from Member member0_ where member0_.MEMBER_ID=? ----- cho 회원님의 주문상품 목록 ----- Hibernate: select products0_.MEMBER_ID as member_i1_1_0_, products0_.PRODUCT_ID as product_2_1_0_, product1_.PRODUCT_ID as product_1_2_1_, product1_.name as name2_2_1_ from MEMBER_PRODUCT products0_ inner join Product product1_ on products0_.PRODUCT_ID=product1_.PRODUCT_ID where products0_.MEMBER_ID=? product = note product = pen
↔️ 양방향
양쪽 엔티티 모두 @ManyToMany 를 사용합니다.
@Entity
@NoArgsConstructor
public class Member {
@Id @GeneratedValue
@Column(name = "MEMBER_ID")
private Long id;
private String username;
@ManyToMany
@JoinTable(name = "MEMBER_PRODUCT",
joinColumns = @JoinColumn(name = "MEMBER_ID"),
inverseJoinColumns = @JoinColumn(name = "PRODUCT_ID"))
private List<Product> products = new ArrayList<Product>();
//getter&setter
//연관관계 편의 메소드
public void addProduct(Product product) {
products.add(product);
if (!product.getMembers().contains(this)) {
product.addMember(this);
}
}
}
@Entity
@NoArgsConstructor
public class Product {
@Id @GeneratedValue
@Column(name = "PRODUCT_ID")
private Long id;
private String name;
@ManyToMany(mappedBy = "products")
private List<Member> members = new ArrayList<Member>();
//getter&setter
//연관관계 편의 메소드
public void addMember(Member member) {
members.add(member);
if (!member.getProducts().contains(this)) {
member.addProduct(this);
}
}
}
// 정방향 탐색
Member cho = em.find(Member.class, member.getId());
System.out.println("----- " + cho.getUsername() + " 회원님의 주문상품 목록 -----");
cho.getProducts().forEach(product -> {
System.out.println("product = " + product.getName());
});
// 역방향 탐색
Product product = em.find(Product.class, note.getId());
System.out.println("-----" + product.getName() + " 상품을 구매한 회원 목록 -----");
product.getMembers().forEach(m -> {
System.out.println("member = " + m.getUsername());
});
다대다 매핑의 한계, 연결 엔티티(관계 테이블)를 사용한 극복
Member 와 Product 의 관계테이블인 member_product 테이블에 날짜, 수량.. 등 컬럼들이 더 필요해지는 요구사항이 있을경우 엔티티로 관리되지 않으면 member_product 에 추가가 어렵기 때문에
관계테이블을 엔티티로 관리하는 것이 좋습니다.
- 복합키를 사용하는 방법
- 대리키를 사용하는 방법
💡 복합키를 사용한 관계 테이블 ( 식별관계 )
부모의 PK(member_id, product_id)를 받아 본인의 PK이자 FK로 사용하는 것을 식별관계라고 합니다.
코드 설명
Member는 주인이 아닙니다. 회원 키를 FK로써 가지고 있는MemberProduct가 주인입니다. 고로Member는mappedBy속성을 사용해야 합니다.Product에서Member로의 탐색 기능이 필요하지 않다고 판단해서 연관관계를 만들지 않음.MemberProduct에는 PK를 매핑하는@Id와 FK를 매핑하는@JoinColumn이 같이 사용 됩니다. 외래키를 기본키로 사용합니다.- 또한
@Id가 2개입니다. 복합키를 사용합니다. JPA에선 복합키를 사용하려면 별도의 클래스를 필요로 합니다. MemberProductId는 복합키 클래스로@IdClass에 명시 해줘야 하며,Serializable을 구현해야 합니다.- 조회를 관계 테이블
MemberProduct의 식별자 클래스MemberProductId로 해야합니다.
@Entity
@NoArgsConstructor
public class Member {
@Id @GeneratedValue
@Column(name = "MEMBER_ID")
private Long id;
private String username;
@OneToMany(mappedBy = "member")
private List<MemberProduct> memberProducts;
}
@Entity
@NoArgsConstructor
public class Product {
@Id @GeneratedValue
@Column(name = "PRODUCT_ID")
private Long id;
private String name;
public Long getId() {
return id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
@Entity
@IdClass(MemberProductId.class)
@NoArgsConstructor
public class MemberProduct {
@Id
@ManyToOne
@JoinColumn(name = "MEMBER_ID")
private Member member;
@Id
@ManyToOne
@JoinColumn(name = "PRODUCT_ID")
private Product product;
private int orderAmount;
private Date orderDate;
}
// 복합키 매핑 클래스
public class MemberProductId implements Serializable {
//MemberProduct에 매핑시킬 객체와 이름이 같아야 합니다.
private Long member;
private Long product;
}
public class _1_Test {
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("myApp");
EntityManager em = emf.createEntityManager();
EntityTransaction tx = em.getTransaction();
tx.begin();
//회원등록
Member member = new Member();
member.setUsername("cho");
em.persist(member);
//상품등록
Product note = new Product();
note.setName("note");
Product pen = new Product();
pen.setName("pen");
em.persist(note);
em.persist(pen);
//상품 주문
MemberProduct memberProduct1 = new MemberProduct();
memberProduct1.setMember(member);
memberProduct1.setProduct(note);
memberProduct1.setOrderAmount(2);
memberProduct1.setOrderDate(new Date());
MemberProduct memberProduct2 = new MemberProduct();
memberProduct2.setMember(member);
memberProduct2.setProduct(pen);
memberProduct2.setOrderAmount(3);
memberProduct2.setOrderDate(new Date());
em.persist(memberProduct1);
em.persist(memberProduct2);
tx.commit();
em.clear();
//회원, 상품조회
MemberProductId memberProductId1 = new MemberProductId();
memberProductId1.setMember(member.getId());
memberProductId1.setProduct(note.getId());
MemberProductId memberProductId2 = new MemberProductId();
memberProductId2.setMember(member.getId());
memberProductId2.setProduct(pen.getId());
MemberProduct findMemberProduct1 = em.find(MemberProduct.class, memberProductId1);
MemberProduct findMemberProduct2 = em.find(MemberProduct.class, memberProductId2);
System.out.println("회원명 : " + findMemberProduct1.getMember().getUsername());
System.out.println("주문 아이템 : " + findMemberProduct1.getProduct().getName());
System.out.println("주문 개수 : " +findMemberProduct1.getOrderAmount());
System.out.println("주문 아이템 : " + findMemberProduct2.getProduct().getName());
System.out.println("주문 개수 : " +findMemberProduct2.getOrderAmount());
}
}
-
JPA LOG
Hibernate: select nextval ('hibernate_sequence') Hibernate: select nextval ('hibernate_sequence') Hibernate: select nextval ('hibernate_sequence') Hibernate: insert into Member (username, MEMBER_ID) values (?, ?) Hibernate: insert into Product (name, PRODUCT_ID) values (?, ?) Hibernate: insert into Product (name, PRODUCT_ID) values (?, ?) Hibernate: insert into MemberProduct (orderAmount, orderDate, MEMBER_ID, PRODUCT_ID) values (?, ?, ?, ?) Hibernate: insert into MemberProduct (orderAmount, orderDate, MEMBER_ID, PRODUCT_ID) values (?, ?, ?, ?) Hibernate: select memberprod0_.MEMBER_ID as member_i1_1_0_, memberprod0_.PRODUCT_ID as product_2_1_0_, memberprod0_.orderAmount as orderamo3_1_0_, memberprod0_.orderDate as orderdat4_1_0_, member1_.MEMBER_ID as member_i1_0_1_, member1_.username as username2_0_1_, product2_.PRODUCT_ID as product_1_2_2_, product2_.name as name2_2_2_ from MemberProduct memberprod0_ inner join Member member1_ on memberprod0_.MEMBER_ID=member1_.MEMBER_ID inner join Product product2_ on memberprod0_.PRODUCT_ID=product2_.PRODUCT_ID where memberprod0_.MEMBER_ID=? and memberprod0_.PRODUCT_ID=? Hibernate: select memberprod0_.MEMBER_ID as member_i1_1_0_, memberprod0_.PRODUCT_ID as product_2_1_0_, memberprod0_.orderAmount as orderamo3_1_0_, memberprod0_.orderDate as orderdat4_1_0_, member1_.MEMBER_ID as member_i1_0_1_, member1_.username as username2_0_1_, product2_.PRODUCT_ID as product_1_2_2_, product2_.name as name2_2_2_ from MemberProduct memberprod0_ inner join Member member1_ on memberprod0_.MEMBER_ID=member1_.MEMBER_ID inner join Product product2_ on memberprod0_.PRODUCT_ID=product2_.PRODUCT_ID where memberprod0_.MEMBER_ID=? and memberprod0_.PRODUCT_ID=? 회원명 : cho 주문 아이템 : note 주문 개수 : 2 주문 아이템 : pen 주문 개수 : 3
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