Saving a Java Object with JPA

• Create a new Student
• Read a Student
• Update a Student
• Delete a Student

💎Student Data Access Object

• Responsible for interfacing with the database
• This is a common design pattern: DAO

hongDemoApp <---> Student DAO <---> database

Student DAO <----> Entity Manager <----> datasource <->database

💎Student DAO Making

• Step1: Define DAO interface

public interface StudentDAO {
	void save(Student theStudent);
    // 여기서 Student는 JPA 엔터티
}

• Step2: Define DAO implementation

public class StudentDAOImpl implements StudentDAO {
	private EntityManager entityManager;
	
    // Inject the entity manager
    @Autowired
    public StudentDAOImpl(EntityManager entityManager) {
    	this.entityManager = entityManager;
    }
    
    // save the Java Object
    @Override
    public void save(Student theStudent) {
    	entityManager.persist(theStudent);
    }
}

• Step3: Update the main App

Specialized Annotation for DAOs

• Spring provides the @Repository annotation

• 코드연습
  Student DAO <----> Entity Manager <----> datasource <->database
  

⚾<1. StudentDAO>

package com.hongJpa.hongdemo.dao;

import com.hongJpa.hongdemo.entity.Student;

public interface StudentDAO {
    void save(Student theStudent);
}

⚾<2. StudentDAOImpl>

package com.hongJpa.hongdemo.dao;

import com.hongJpa.hongdemo.entity.Student;
import jakarta.persistence.EntityManager;
import jakarta.transaction.Transactional;
import org.springframework.stereotype.Repository;

@Repository
public class StudentDAOImpl implements StudentDAO{
    // define field for entity manager
    private final EntityManager entityManager;

    // inject entity manager using constructor injection
    public StudentDAOImpl(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    // implement save method
    @Override
    @Transactional
    public void save(Student theStudent) {
        entityManager.persist(theStudent);
    }
}

⚾<3. 실행>

package com.hongJpa.hongdemo;

import com.hongJpa.hongdemo.dao.StudentDAO;
import com.hongJpa.hongdemo.entity.Student;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class HongdemoApplication {

	public static void main(String[] args) {
		SpringApplication.run(HongdemoApplication.class, args);
	}

	@Bean
	public CommandLineRunner commandLineRunner(StudentDAO studentDAO) {
		return runner -> {
			createStudent(studentDAO);
		};
	}

	private void createStudent(StudentDAO studentDAO) {
		// create the student object
		System.out.println("Creating new Student object...");

		Student tempStudent = new Student("hongkyu", "Ryu", "minsubrother@naver.com");

		// save the student object
		System.out.println("saving the students");
		studentDAO.save(tempStudent);

		// display id of the saved student
		System.out.println("saved Student Generated id: " + tempStudent.getId());

	}
}

⚾<4.결과>