[Spring] Deleteing Objects with JPA

Deleting Objects with JPA Overview

• Hibernate/JPA CRUD (8)

Delete a Student

// retrieve the student
int id = 1;
Student theStudent = entityManager.find(Student.class, id);

// delete the student
entityManager.remove(theStudent);

Delete based on a condition

Delete All Students

int numRowsDeleted = entityManager.createQuery("DELETE FROM Student").excuteUpdate();

Development Process

1. Add new method to DAO interface
2. Add new method to DAO implemen
3. Update main app

Step 1: Add new method to DAO interface

public interface StudentDAO {
	void delete(Integer id);
}

Step 2: Define DAO implementation

@Repository  
public class StudentDAOImpl implements StudentDAO{  
    private EntityManager entityManager;
    ...
	@Override  
	@Transactional  // <- Add @Transactional since we are performing a delete
	public void delete(Integer id) {  
	    // retrieve the student  
	    Student theStudent = entityManager.find(Student.class, id);  
	    // delete the student  
	    entityManager.remove(theStudent);  
}

Step 3: Update main app

@SpringBootApplication  
public class CruddemoApplication {
	...
	public CommandLineRunner commandLineRunner(StudentDAO studentDAO){  
	   return runner-> {
	          deleteAllStudents(studentDAO);  
   };  
}
private void deleteStudent(StudentDAO studentDAO) {  
   int studentId = 2;  
   System.out.println("Deleting student id: " + studentId);  
   studentDAO.delete(studentId);  
}

Delete all of the students

public interface StudentDAO {
	int deleteAll();
}

private void deleteAllStudents(StudentDAO studentDAO) {  
   System.out.println("Deleting all students");  
   int numRowsDeleted = studentDAO.deleteAll();  
   System.out.println("Deleted row count: " + numRowsDeleted);  
}