1.조인 전략
- 각각 테이블 생성
- 어노테이션 추가: @Inheritance(strategy = InheritanceType.JOINED)
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class Item {
@Id
@GeneratedValue
private Long id;
private String name;
private int price;
}Hibernate:
create table Album (
artist varchar(255),
id bigint not null,
primary key (id)
)
Hibernate:
create table Book (
author varchar(255),
isbn varchar(255),
id bigint not null,
primary key (id)
)
Hibernate:
create table Item (
id bigint not null,
name varchar(255),
price integer not null,
primary key (id)
)
Hibernate:
create table Movie (
actor varchar(255),
director varchar(255),
id bigint not null,
primary key (id)
)- 등록
public class jpaMain {
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");
EntityManager em = emf.createEntityManager();
EntityTransaction tx = em.getTransaction();
tx.begin();
try {
//movie 등록
Movie movie = new Movie();
movie.setDirector("a");
movie.setActor("b");
movie.setName("트루먼쇼");
movie.setPrice(10000);
em.persist(movie);
tx.commit();
} catch (Exception e) {
tx.rollback();
} finally {
em.close();
}
emf.close();
}
}Hibernate:
/* insert hellojpa.mappingAdvanced.Movie
*/ insert
into
Item
(name, price, id)
values
(?, ?, ?)
Hibernate:
/* insert hellojpa.mappingAdvanced.Movie
*/ insert
into
Movie
(actor, director, id)
values
(?, ?, ?)- 조회
- 조인해서 값을 가져옴
public class jpaMain {
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");
EntityManager em = emf.createEntityManager();
EntityTransaction tx = em.getTransaction();
tx.begin();
try {
//movie 등록
Movie movie = new Movie();
movie.setDirector("a");
movie.setActor("b");
movie.setName("트루먼쇼");
movie.setPrice(10000);
em.persist(movie);
//movie 조회
em.flush();
em.clear(); //영속성 컨텍스트 비우기(1차캐시도 삭제)
Movie findMovie = em.find(Movie.class, movie.getId());
System.out.println("findMovie = " + findMovie);
tx.commit();
} catch (Exception e) {
tx.rollback();
} finally {
em.close();
}
emf.close();
}
}Hibernate:
select
movie0_.id as id1_2_0_,
movie0_1_.name as name2_2_0_,
movie0_1_.price as price3_2_0_,
movie0_.actor as actor1_10_0_,
movie0_.director as director2_10_0_
from
Movie movie0_
inner join
Item movie0_1_
on movie0_.id=movie0_1_.id
where
movie0_.id=?
findMovie = hellojpa.mappingAdvanced.Movie@51ec2df1- 구분타입(DTYPE)
- 부모클래스에 @DiscriminatorColum 어노테이션 추가
- (기본)부모테이블에 "DTYPE"이라는 컬럼을 생성하여 "자식 엔티티명"을 입력
- (컬럼명 변경)부모클래스에 @DiscriminatorColumn(name = "XXX")
- (입력값 변경)엔티티명이 아닌 값을 입력하고 싶을 경우 자식클래스에 @DiscriminatorValue("XXX")
📌조인 전략에서는 구분타입 추가는 optional(그래도 실무에서는 사용을 권장)
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn
public abstract class Item {
@Id
@GeneratedValue
private Long id;
private String name;
private int price;
}
2.단일 테이블 전략
- 어노테이션 미추가시 JPA가 사용하게 되는 기본전략
- 부모 테이블에 모든 컬럼 생성
@Entity
public abstract class Item {
@Id
@GeneratedValue
private Long id;
private String name;
private int price;
}@Entity
public class Album extends Item {
private String artist;
}@Entity
public class Movie extends Item {
private String director;
private String actor;
}@Entity
public class Book extends Item {
private String author;
private String isbn;
}Hibernate:
create table Item (
DTYPE varchar(31) not null,
id bigint not null,
name varchar(255),
price integer not null,
actor varchar(255),
director varchar(255),
author varchar(255),
isbn varchar(255),
artist varchar(255),
primary key (id)
)- 등록, 조회 모두 심플하게 쿼리가 한 번만 실행됨
Hibernate:
/* insert hellojpa.mappingAdvanced.Movie
*/ insert
into
Item
(name, price, actor, director, DTYPE, id)
values
(?, ?, ?, ?, 'Movie', ?)
Hibernate:
select
movie0_.id as id2_0_0_,
movie0_.name as name3_0_0_,
movie0_.price as price4_0_0_,
movie0_.actor as actor5_0_0_,
movie0_.director as director6_0_0_
from
Item movie0_
where
movie0_.id=?
and movie0_.DTYPE='Movie'
📌단일 테이블 전략에서는 구분타입이 자동으로 추가됨(어노테이션 안 붙여도)
3.구현 클래스마다 테이블 전략
- 필요한 속성들을 클래스마다 중복되게 생성
- 어노테이션 추가: @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
@DiscriminatorColumn
public abstract class Item {
@Id
@GeneratedValue
private Long id;
private String name;
private int price;
}Hibernate:
create table Movie (
id bigint not null,
name varchar(255),
price integer not null,
actor varchar(255),
director varchar(255),
primary key (id)
)
- 등록, 조회시 필요한 값들을 movie 테이블 하나에서 다 해결
Hibernate:
/* insert hellojpa.mappingAdvanced.Movie
*/ insert
into
Movie
(name, price, actor, director, id)
values
(?, ?, ?, ?, ?)
Hibernate:
select
movie0_.id as id1_2_0_,
movie0_.name as name2_2_0_,
movie0_.price as price3_2_0_,
movie0_.actor as actor1_10_0_,
movie0_.director as director2_10_0_
from
Movie movie0_
where
movie0_.id=?
📌구현 클래스마다 테이블 전략에서는 구분타입 추가가 무의미(추가해도 적용안됨)
