20241101 53일차

현업에서는 즉시로딩보다는 지연로딩을 주로 씀

이론상으로는 즉시로딩을 권장하지만 실무에서는 지연로딩을 씀

 

실습

 

 

Department.java

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "id")
private Company company;

 

Employee.java

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "dept_id")
private Department department;

 

DB

employee 테이블

department 테이블

company 테이블

package jpajava;

import domain.Company;
import domain.Department;
import domain.Employee;

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

public class Emp_Dept_Company_Test {
  public static void main(String[] args) {
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("jpatest");
    EntityManager em = emf.createEntityManager();
    EntityTransaction tx = em.getTransaction();
    
    tx.begin();
    System.out.println("Transaction START!");
    try {
//      Company company = new Company();
//      company.setName("KOSTA");
//      em.persist(company);
//      System.out.println("company 생성");
//
//      Department dept = new Department();
//      dept.setDeptName("Sales"); // 비영속 상태
//      dept.setCompany(company);
//      em.persist(dept); // 영속 상태, 즉시 쓰기
//      System.out.println("dept 생성");

      Employee employee = em.find(Employee.class, "202403");
      System.out.println("employee.getEmpName() = " + employee.getEmpName());
      System.out.println("employee.getDepartment().getClass() = " + employee.getDepartment().getClass());
      System.out.println("--------------- id 출력 전 --------------- ");
      System.out.println("employee.getDepartment().getDeptId() = " + employee.getDepartment().getDeptId());
      System.out.println("--------------- deptName 출력 전 --------------- ");
      System.out.println("employee.getDepartment().getDeptName() = " + employee.getDepartment().getDeptName());
      System.out.println("employee.getDepartment().getClass() = " + employee.getDepartment().getClass());
      System.out.println("employee.getDepartment().getDeptId() = " + employee.getDepartment().getDeptId());

      System.out.println("commit 전");
      tx.commit();
      System.out.println("commit 후");
    } catch (Exception e) {
      tx.rollback();
      System.out.println();
      System.out.println("[Error] : " + e.getMessage());
    } finally {
      System.out.println("Transaction COMPLETED!");
    }
  }
}

• proxy

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즉시로딩과 N+1 쿼리 문제

 

JPQL Fetch Join - 중요!!!!!!