[java] JPA Embeddable

By starseat
2022-10-26 08:53:17
java/spring

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# JPA Embeddable

아래와 같은 테이블 구조 중 `address1`, `address2`, `zipcode` 를 `Address` 라는 class 로 분리하고자 할 때 사용

![image.png](/uploads/_temp/20221026/9fdccb00fb4c542534a6753b39058e0d.png)

## @Embeddable

- Entity 가 아닌 타입을 한 개 이상의 필드와 매핑할 대 사용
  -  예: Address, Money 등 묶을 수 있는 세부 속성
- Entity 의 한 속성으로 @Embeddable 적용 타입 사용

```java
@Embeddable
public class Address {
  @Column(name = "addr1")
  private String address1;
  
  @Column(name = "addr2")
  private String address2;
  
  @Column(name = "zipcode")
  private String zipcode;
  
  ...
}
```

```java
@Entity
@Table(name = "user_info")
public class User {
  @Id
  @Column(name = "user_id")
  private String id;
  
  ...
  
  @Embedded
  private Address address;
}
```

### 사용 예

#### 생성

```java
tx.begin();

Address address = new Address("주소 1", "주소 2", "12345");
User user = new User("10001", ..., address);
em.persist(user);

tx.commit();
```

- Address 가 `null` 일 때는 해당 값들이 `DB` 에 `null` 로 들어감

```java
tx.begin();

Address address = null;
User user = new User("10002", ..., address);
em.persist(user);

tx.commit();
```

#### 조회

```java
User user = em.find(User.class, "10001");
logger.info("주소: {}", user.getAddress());
```

- 조회도 `Address` 가 `null` 일 경우 `Address` 객체가 `null` 임.

```
User user = em.find(User.class, "10002");
boolean isAddr = user.getAddress() == null; // true
```

## 같은 @Embeddable 타입 필드가 두개면?

```java
@Entity
public class Employee {
  @Id
  private String id;
  
  @Embedded private Address homeAddress;
  @Embedded private Address workAddress;
}
```

위와 같은 경우라면 `org.hibernate.MappingException` 이 발생함.
이 경우는 `@AttributeOverride` 로 설정 재정의 해야함.

## @AttributeOverride 설정 재정의

```java
@Entity
public class Employee {
  @Id
  private String id;
  
  @Embedded
  private Address homeAddress;
  
  @AttributeOverrides({
    @AttributeOverride(name = "address1", column = @Column(name = "waddr1")),
    @AttributeOverride(name = "address2", column = @Column(name = "waddr2")),
    @AttributeOverride(name = "zipcode", column = @Column(name = "wzipcode")),
  })
  @Embedded
  private Address workAddress;
  
  ...
}
```

## 다른 테이블에 값을 저장할 때

![image.png](/uploads/_temp/20221026/e8b2098c41cf7281547278b047facc2c.png)

### 방법 1 : @SecondaryTable + 테이블 명

```java
@Embeddable
public class Intro {
  @Column(
    table = "writer_intro",
    name = "content_type"
  )
  private String contentType;
  
  @Column(table = "writer_intro")
  private String content;
}
```

```java
@Entity
@SecondaryTable(
  name = "writer_intro",
  pkJoinColumns = @PrimaryKeyJoinColumn(
    name = "writer_id",          // writer_intro 테이블 컬럼
    referencedColumnName = "id"  // writer 테이블 컬럼
  )
)
public class Writer {
  ...
  
  @Embedded
  private Intro intro;
  
  ...
}
```

### 방법 2 : @SecondaryTable + @AttributeOverride

```java
@Entity
@SecondaryTables({
  @SecondaryTables(
    name = "writer_intro",
    pkJoinColumns = @PrimaryKeyJoinColumn(name = "writer_id", referencedColumnName = "id")
  ),
  ...
})
public class Writer {
  ...
  
  @Embedded
  @AttributeOverrides({
    @AttributeOverride(name = "address1", column = @Column(table = "writer_address", name = "addr1")),
    @AttributeOverride(name = "address2", column = @Column(table = "writer_address", name = "addr2")),
    @AttributeOverride(name = "zipcode", column = @Column(table = "writer_address")
  })
  private Address address;
}
```

### 사용 예

- 저장

```java
Writer w = new Writer(
  "name",
  new Address("주소 1", "주소 2", "12345"),
  new Intro("text/plain", "테스트")
);
em.persist(w);
```

```sql
insert into writer (name) values (?)
insert into writer_address (addr1, addr2, zipcode, writer_id) value (?, ?, ?, ?)
insert into writer_intro (content, content_type, writer_id) value (?, ?, ?)
```

- 저장 2 : intro 값이 null 일 경우

```java
Writer w = new Writer(
  "name2",
  new Address("주소 1", "주소 2", "12345"),
  null
);
em.persist(w);
```

```sql
insert into writer (name) values (?)
insert into writer_address (addr1, addr2, zipcode, writer_id) value (?, ?, ?, ?)
```

- 조회 : `left join` 사용
  - `inner join` 을 사용할 경우 @Embeddable 항목이 없을 경우 조회가 안됨.

```java
Writer writer = em.find(Writer.class, id);
```

```sql
select
  w1_0.id,w1_0,name,w1_1.addr1,w1_1.addr2,w1_1.zipcode,w1_2.content,w1_2.content_type
from writer w1_0
left join writer_address w1_1 on w1_0.id=w1_1.writer_id
left join writer_intro w1_2 on w1_0.id=w2_2.writer_id
where w1_0.id=?
```

- 변경 1 : Address 에 값 지정

```java
Writer writer = em.find(Writer.class, id);
writer.setAddress(new Address("새 주소 1", "새 주소 2", "12345"));
```

```sql
-- address 가 null 이 아닌 값이 존재할 경우
update writer_address set addr1=?, addr2=?, zipcode=? where writer_id?

-- address 가 null 이었을 경우
insert into writer_address (addr1, addr2, zipcode, writer_id) values (?, ?, ?, ?)
```

- 변경 2 : Address 에 null 지정

```java
Writer writer = em.find(Writer.class, id);
writer.setAddress(null);
```

```sql
-- address 가 null 이 아닌 값이 존재할 경우
delete from writer_address where writer_id=?
```

- 삭제

```java
Writer writer = em.find(Writer.class, id);
em.remove(writer);
```

```sql
delete from writer_intro where writer_id=?
delete from writer_address where writer_id=?
delete from writer where id=?
```

# 출처

- [최범균님의 JPA 기초 06 @Embeddable](https://www.youtube.com/watch?v=WtS5IszIueA)
- [최범균님의 JPA 기초 07 @Embeddable2](https://www.youtube.com/watch?v=3_sdQGfL2Lg)

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