[Spring] @GeneratedValue | 엔티티의 기본 키 생성 전략

 

🔍 @GeneratedValue

/*
 * Copyright (c) 2008, 2020 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Linda DeMichiel - 2.1
//     Linda DeMichiel - 2.0

package jakarta.persistence;

import java.lang.annotation.Target;
import java.lang.annotation.Retention;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static jakarta.persistence.GenerationType.AUTO;

/**
 * Provides for the specification of generation strategies for the
 * values of primary keys. 
 *
 * <p> The <code>GeneratedValue</code> annotation
 * may be applied to a primary key property or field of an entity or
 * mapped superclass in conjunction with the {@link Id} annotation.
 * The use of the <code>GeneratedValue</code> annotation is only
 * required to be supported for simple primary keys.  Use of the
 * <code>GeneratedValue</code> annotation is not supported for derived
 * primary keys.
 *
 * <pre>
 *
 *     Example 1:
 *
 *     &#064;Id
 *     &#064;GeneratedValue(strategy=SEQUENCE, generator="CUST_SEQ")
 *     &#064;Column(name="CUST_ID")
 *     public Long getId() { return id; }
 *
 *     Example 2:
 *
 *     &#064;Id
 *     &#064;GeneratedValue(strategy=TABLE, generator="CUST_GEN")
 *     &#064;Column(name="CUST_ID")
 *     Long id;
 * </pre>
 *
 * @see Id
 * @see TableGenerator
 * @see SequenceGenerator
 *
 * @since 1.0
 */
@Target({METHOD, FIELD})
@Retention(RUNTIME)

public @interface GeneratedValue {

    /**
     * (Optional) The primary key generation strategy
     * that the persistence provider must use to
     * generate the annotated entity primary key.
     */
    GenerationType strategy() default AUTO;

    /**
     * (Optional) The name of the primary key generator
     * to use as specified in the {@link SequenceGenerator} 
     * or {@link TableGenerator} annotation.
     * <p> Defaults to the id generator supplied by persistence provider.
     */
    String generator() default "";
}

 

🔍 GenerationType

/*
 * Copyright (c) 2008, 2022 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Linda DeMichiel - 2.1
//     Linda DeMichiel - 2.0

package jakarta.persistence;

/** 
 * Defines the types of primary key generation strategies. 
 *
 * @see GeneratedValue
 *
 * @since 1.0
 */
public enum GenerationType { 

    /**
     * Indicates that the persistence provider must assign 
     * primary keys for the entity using an underlying 
     * database table to ensure uniqueness.
     */
    TABLE, 

    /**
     * Indicates that the persistence provider must assign 
     * primary keys for the entity using a database sequence.
     */
    SEQUENCE, 

    /**
     * Indicates that the persistence provider must assign 
     * primary keys for the entity using a database identity column.
     */
    IDENTITY,

    /**
     * Indicates that the persistence provider must assign
     * primary keys for the entity by generating an RFC 4122
     * Universally Unique IDentifier.
     */
    UUID,

    /**
     * Indicates that the persistence provider should pick an 
     * appropriate strategy for the particular database. The 
     * <code>AUTO</code> generation strategy may expect a database 
     * resource to exist, or it may attempt to create one. A vendor 
     * may provide documentation on how to create such resources 
     * in the event that it does not support schema generation 
     * or cannot create the schema resource at runtime.
     */
    AUTO
}

GenerationType은 enum 타입으로 TABLE, SEQUENCE, IDENTITY, UUID, AUTO 5개의 값을 가질 수 있다.

• TABLE: 데이터베이스에 키 생성 전용 테이블을 하나 만들고 이를 사용하여 기본키 생성
• SEQUENCE: 데이터베이스의 특별한 오브젝트 시퀀스를 사용하여 기본키 생성
• IDENTITY: 기본키 생성을 데이터베이스에 위임 ex) MySQL - AUTO_INCREMENT
• AUTO: JPA 구현체가 자동으로 생성 전략 결정

---

🔍 어떤 전략을 사용해야 하는가?

Entity의 Primary Key는 Long 타입의 Auto_increment를 사용하는 게 좋다.

주민등록번호와 같이 비즈니스상 Unique Key나, 여러 키를 조합한 복합키로 PK를 잡을 경우 난감한 상황이 종종 발생한다.

• Foriegn Key를 맺을 때 다른 테이블에서 복합키 전부를 갖고 있거나, 중간 테이블을 하나 더 둬야 하는 상황 발생
• 인덱스에 좋은 영향 X
• 유니크한 조건이 변경될 경우 PK 전체를 수정해야 하는 일 발생

* 주민등록번호, 복합키 등은 Unique Key로 별도로 추가하는 것이 좋다

 

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📋 참고 자료

GeneratedValue (Java(TM) EE 7 Specification APIs)

@Id / @GeneratedValue에 대해 알아보자

+ 스프링 부트와 AWS로 혼자 구현하는 웹 서비스