Chapter 07. 엔티티 매핑

@Entity
public class Member {
    @Id
    private Long id;
    private String username;
}

@Entity
public class Member {

    // 기본 생성자 필수!
    protected Member() {}

    public Member(String username) {
        this.username = username;
    }
}

@Entity
@Table(name = "MEMBER",
       schema = "public",
       uniqueConstraints = {
           @UniqueConstraint(
               name = "UK_MEMBER_EMAIL",
               columnNames = {"email"}
           )
       })
public class Member { ... }

@Entity
public class Member {
    @Id
    private String id;  // 직접 할당

    private String username;
}

// 사용
Member member = new Member();
member.setId("user001");  // 직접 설정 필수!
em.persist(member);

@Entity
public class Member {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
}

@Entity
@SequenceGenerator(
    name = "MEMBER_SEQ_GENERATOR",
    sequenceName = "MEMBER_SEQ",
    initialValue = 1,
    allocationSize = 50  // 성능 최적화!
)
public class Member {
    @Id
    @GeneratedValue(
        strategy = GenerationType.SEQUENCE,
        generator = "MEMBER_SEQ_GENERATOR"
    )
    private Long id;
}

// allocationSize = 50 설정 시
// 1. 첫 persist(): DB 시퀀스에서 1~50 할당
// 2. 메모리에서 1~50 사용 (DB 조회 없음!)
// 3. 51번째 persist(): DB에서 51~100 할당

@Entity
@TableGenerator(
    name = "MEMBER_SEQ_GENERATOR",
    table = "MY_SEQUENCES",
    pkColumnName = "sequence_name",
    valueColumnName = "next_val",
    pkColumnValue = "MEMBER_SEQ",
    allocationSize = 1
)
public class Member {
    @Id
    @GeneratedValue(
        strategy = GenerationType.TABLE,
        generator = "MEMBER_SEQ_GENERATOR"
    )
    private Long id;
}

CREATE TABLE MY_SEQUENCES (
    sequence_name VARCHAR(255) NOT NULL,
    next_val BIGINT,
    PRIMARY KEY (sequence_name)
);

-- 데이터
-- MEMBER_SEQ | 100

@Entity
public class Member {
    @Id
    @GeneratedValue  // strategy 생략 시 AUTO
    private Long id;
}

// MySQL 사용 시
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

// Oracle 사용 시
@SequenceGenerator(allocationSize = 50)  // 성능 최적화!
@GeneratedValue(strategy = GenerationType.SEQUENCE)
private Long id;

@Entity
public class Member {
    @Id
    private Long id;

    @Column(
        name = "username",           // 컬럼명
        nullable = false,            // NOT NULL
        length = 50,                 // VARCHAR(50)
        unique = true,               // UNIQUE 제약
        columnDefinition = "VARCHAR(100) DEFAULT 'EMPTY'"  // DDL 직접 정의
    )
    private String username;

    @Column(precision = 10, scale = 2)  // DECIMAL(10,2)
    private BigDecimal salary;
}

int age;        // → age integer NOT NULL (기본형)
Integer age;    // → age integer (객체형, null 가능)
String name;    // → name varchar(255)

public enum RoleType {
    ADMIN, USER, GUEST
}

@Entity
public class Member {
    @Enumerated(EnumType.STRING)  // 반드시 STRING!
    private RoleType roleType;
}

// 초기 상태
enum RoleType { ADMIN, USER }  // ADMIN=0, USER=1

// DB 저장
member.setRoleType(ADMIN);  // → DB에 0 저장

// 나중에 Enum 수정
enum RoleType { GUEST, ADMIN, USER }  // GUEST=0, ADMIN=1, USER=2

// 기존 데이터 조회
// DB의 0은 이제 GUEST로 조회됨! (원래는 ADMIN) 💥

@Temporal(TemporalType.DATE)
private Date birthDate;  // 날짜만: 2025-12-19

@Temporal(TemporalType.TIME)
private Date wakeUpTime;  // 시간만: 14:30:00

@Temporal(TemporalType.TIMESTAMP)
private Date createdDate;  // 날짜+시간: 2025-12-19 14:30:00

@Entity
public class Member {
    private LocalDate birthDate;           // @Temporal 불필요!
    private LocalTime wakeUpTime;          // @Temporal 불필요!
    private LocalDateTime createdDateTime; // @Temporal 불필요!
    private ZonedDateTime registeredAt;    // 타임존 포함
}

@Entity
public class Article {
    @Id
    private Long id;

    @Lob
    private String content;  // CLOB (문자형)

    @Lob
    private byte[] thumbnail;  // BLOB (바이너리)
}

@Entity
public class Member {
    @Id
    private Long id;

    private String username;

    @Transient
    private int temp;  // DB에 저장 안 됨, 메모리에서만 사용
}

<!-- persistence.xml -->
<property name="hibernate.hbm2ddl.auto" value="create" />

<!-- 카멜케이스 → 언더스코어 자동 변환 -->
<property name="hibernate.ejb.naming_strategy"
          value="org.hibernate.cfg.ImprovedNamingStrategy"/>

// Java
private LocalDateTime createdDate;

// DB 컬럼
created_date

package com.example.entity;

import javax.persistence.*;
import java.math.BigDecimal;
import java.time.LocalDateTime;

@Entity
@Table(name = "MEMBER",
       uniqueConstraints = {
           @UniqueConstraint(
               name = "UK_MEMBER_EMAIL",
               columnNames = "email"
           )
       })
public class Member {

    // 기본 키 - IDENTITY 전략 (MySQL)
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "member_id")
    private Long id;

    // 필수 문자열 필드
    @Column(name = "username", nullable = false, length = 50)
    private String username;

    @Column(name = "email", nullable = false, length = 100)
    private String email;

    // NULL 가능 필드 (Integer 사용)
    @Column(name = "age")
    private Integer age;

    // Enum 타입 - 반드시 STRING
    @Enumerated(EnumType.STRING)
    @Column(name = "role_type", nullable = false, length = 20)
    private RoleType roleType;

    // 대용량 텍스트
    @Lob
    @Column(name = "description")
    private String description;

    // 날짜 타입 - Java 8+
    private LocalDateTime createdDate;
    private LocalDateTime lastModifiedDate;

    // 매핑 제외
    @Transient
    private String tempData;

    // 기본 생성자 (JPA 필수!)
    protected Member() {}

    // 생성자
    public Member(String username, String email, RoleType roleType) {
        this.username = username;
        this.email = email;
        this.roleType = roleType;
        this.createdDate = LocalDateTime.now();
        this.lastModifiedDate = LocalDateTime.now();
    }

    // Getter, Setter
    public Long getId() { return id; }
    public String getUsername() { return username; }
    public void setUsername(String username) {
        this.username = username;
        this.lastModifiedDate = LocalDateTime.now();
    }
    // ... 나머지 getter/setter
}

enum RoleType {
    ADMIN, USER, GUEST
}

CREATE TABLE MEMBER (
    member_id BIGINT NOT NULL AUTO_INCREMENT,
    username VARCHAR(50) NOT NULL,
    email VARCHAR(100) NOT NULL,
    age INTEGER,
    role_type VARCHAR(20) NOT NULL,
    description CLOB,
    created_date TIMESTAMP,
    last_modified_date TIMESTAMP,
    PRIMARY KEY (member_id),
    CONSTRAINT UK_MEMBER_EMAIL UNIQUE (email)
);

// MySQL 환경
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

// Oracle 환경 (성능 최적화)
@SequenceGenerator(
    name = "SEQ_GEN",
    sequenceName = "MEMBER_SEQ",
    allocationSize = 50
)
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_GEN")
private Long id;

// 개발 초기 (DB 미정)
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;