[Spring JPA] Hello 순수JPA

 

목차

• 프로젝트 생성
• 애플리케이션 개발

 

1. 프로젝트 생성

DB: H2 Database

H2Database 설정은 이전 포스팅에 있다. (xml에서 H2db 버전은 맞춰야 한다)

IDE: IntelliJ

Project: Maven

 

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>jpa-basic</groupId>
<artifactId>ex1-hello-jpa</artifactId>
<version>1.0.0</version>
<dependencies>
    <!-- JPA 하이버네이트 -->
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-entitymanager</artifactId>
        <version>5.3.10.Final</version>
    </dependency>
    <!-- H2 데이터베이스 -->
    <dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <version>2.1.214</version>
    </dependency>
    <dependency>
        <groupId>javax.xml.bind</groupId>
        <artifactId>jaxb-api</artifactId>
        <version>2.3.0</version>
    </dependency>
</dependencies>
    <properties>
        <maven.compiler.source>18</maven.compiler.source>
        <maven.compiler.target>18</maven.compiler.target>
    </properties>
</project>

본 프로젝트는 Spring을 이용하지 않기때문에 버전은 크게 상관없다. (xml에서 H2db 버전은 맞춰야 한다)

 

Resouces > META-INF > persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.2"
             xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd">
    <persistence-unit name="hello">
        <properties>
            <!-- 필수 속성 -->
            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
            <property name="javax.persistence.jdbc.user" value="sa"/>
            <property name="javax.persistence.jdbc.password" value=""/>
            <property name="javax.persistence.jdbc.url" value="jdbc:h2:tcp://localhost/~/test"/>
            <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
            <!-- 옵션 -->
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>
            <property name="hibernate.use_sql_comments" value="true"/>
            <!--<property name="hibernate.hbm2ddl.auto" value="create" />-->
        </properties>
    </persistence-unit>
</persistence>

대상 바이트코드 변경 1.5 -> 8

 

2. 애플리케이션 개발

JPA 동작 방식

JpaMain 클래스 생성

package hellojpa;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class jpaMain {
    public static void main(String[] args) {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");

        EntityManager em = emf.createEntityManager();

        //code

        emf.close();

        em.close();
    }
}

H2 database 테이블 생성

DB와 매핑되는 클래스 만들기

package hellojpa;

import javax.persistence.*;

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

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

 

Main 변경

package hellojpa;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;

public class jpaMain {
    public static void main(String[] args) {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");

        EntityManager em = emf.createEntityManager();

        EntityTransaction tx = em.getTransaction();
        tx.begin();

        //code start
        Member member = new Member();
        member.setId(1L);
        member.setName("hello");
        em.persist(member);

        //code end

        tx.commit();

        emf.close();

        em.close();
    }
}

 

DB 결과물

JPA가 매핑정보를 보고 쿼리를 작성해준다.

 

 

정석 Main code (Create)

package hellojpa;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;

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 {
            Member member = new Member();
            member.setId(1L);
            member.setName("hello");

            em.persist(member);

            tx.commit();
        } catch (Exception e){
            tx.rollback();
        } finally {
            em.close();
        }
        emf.close();
    }
}

 

Read 코드

package hellojpa;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;

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 {
            Member member = new Member();
            member.setId(1L);
            member.setName("hello");

            em.persist(member);

            Member findMember = em.find(Member.class, 1L);
            System.out.println("findMember.getName() = " + findMember.getName());
            System.out.println("findMember.getId() = " + findMember.getId());
            
            tx.commit();
        } catch (Exception e){
            tx.rollback();
        } finally {
            em.close();
        }
        emf.close();
    }
}

 

Delete 코드

em.remove(findMember);

을 이용하여 삭제하면 된다.

 

Update 코드

package hellojpa;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;

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 {
            Member findMember = em.find(Member.class, 1L);
            findMember.setName("helloJPA");

            tx.commit();
        } catch (Exception e){
            tx.rollback();
        } finally {
            em.close();
        }
        emf.close();
    }
}

DB결과

 

 

멤버 객체를 대상으로 쿼리를 구성 (JPQL)

package hellojpa;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;
import java.util.List;

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 {
//            Member member = new Member();
//            member.setId(1L);
//            member.setName("hello");
//
//            em.persist(member);
//
//            Member findMember = em.find(Member.class, 1L);
//            findMember.setName("helloJPA");
//            em.remove(findMember);

            //멤버 객체를 대상으로 쿼리를 구성 (JPQAL)
            List<Member> result = em.createQuery("select m from Member as m", Member.class)
                    .getResultList();
            for (Member member : result) {
                System.out.println("member.getName() = " + member.getName());
            }

            tx.commit();
        } catch (Exception e){
            tx.rollback();
        } finally {
            em.close();
        }
        emf.close();
    }
}

 

JPA는 SQL을 추상화한 JPQL이라는 객체 지향 쿼리 언어를 제공해준다.

JPQL은 SQL과 유사한 문법을 가지고 있으며, SELECT, FROM, WHERE, GROUP BY, HAVING, JOIN 등을 지원한다.

또한 JPQL은 엔티티 객체를 대상으로 쿼리를 작성. <-> SQL은 데이터베이스 테이블을 대상으로 쿼리를 작성

 

한마디로, JPQL은 객체 지향 SQL이라고 생각하면 될 듯하다.