JPA 프로젝트 시작하기

jpa 설정을 완료하고 CRUD 를 실습해보자.

Member table을 만들어주자.

그 다음은 Member class를 만들어주자.

package hellojpa;

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

@Entity
public class Member {

    @Id
    private Long id;
    private String name;

    public String getName() {
        return name;
    }

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

    public Long getId() {
        return id;
    }

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

그 다음은 데이터베이스와 연결해서 값을 넣어보자.

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("x");
        EntityManager em = emf.createEntityManager();

        EntityTransaction tx = em.getTransaction();
        tx.begin();
        Member member = new Member();
        member.setId(1L);
        member.setName("jpaStart");
        try {
            em.persist(member);
            tx.commit();
        } catch (Exception e) {
            tx.rollback();
        } finally {
            em.close();
            emf.close();
        }
    }
}

삽입이 잘 되었음을 알 수 있다.

다른 객체들도 만들어서 넣어줘서 조회, 삭제, 수정을 연습해보자.

조회를 해보자.

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("x");
        EntityManager em = emf.createEntityManager();

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

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

실행하면 쿼리가 나오고 그리고 System.out.println 한 부분이 나오게 된다.

삭제를 해보자.

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("x");
        EntityManager em = emf.createEntityManager();

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

        try {
            Member member = em.find(Member.class, 1L);
            em.remove(member);
            tx.commit();
        } catch (Exception e) {
            tx.rollback();
        } finally {
            em.close();
            emf.close();
        }
    }
}

삭제된 것을 알 수 있다.

 

 

수정을 해보자

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("x");
        EntityManager em = emf.createEntityManager();

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

        try {
            Member member = em.find(Member.class, 2L);
            member.setName("Fix to A");
            tx.commit();
        } catch (Exception e) {
            tx.rollback();
        } finally {
            em.close();
            emf.close();
        }
    }
}

Member의 setName을 호출하였는데도 Update 쿼리가 나온다. 실제로 데이터베이스를 확인하자.

em.persist 함수를 부르지 않아도 id가 2인 Member의 네임이 수정되었다.

 

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("x");
        EntityManager em = emf.createEntityManager();

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

        try {
            List<Member> result = em.createQuery("select m from Member as m", Member.class).getResultList();
            System.out.println(result.size());
            for (Member member : result) {
                System.out.println(member.getName());
            }
            tx.commit();
        } catch (Exception e) {
            tx.rollback();
        } finally {
            em.close();
            emf.close();
        }
    }
}

query문을 직접 실행할 수도 있다. JPQL 이라고 부른다.