1. JPA 시작하기

1. 프로젝트 생성하기

• 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>5.6.1.Final</version>
        </dependency>
        <!-- H2 데이터베이스 -->
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <version>2.0.202</version>  >>> 실제 사용하고 있는 버전과 동일
        </dependency>
    </dependencies>
</project>

• 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"/>

```

• main.class

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

• Entity.class

package hellojpa;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
//@Table(name = "user") >> 테이블 이름 지정
public class Member {

    @Id
    private Long id;
		//@Column(name ="username") >> 속성 명 지정
    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;
    }


}

• JPA는 트랜젝션이 중요하다!! EntityManager에서 트랜젝션을 받아와 시작과 롤백 커밋을 해줘야한다!!