[Spring] Reading Objects with JPA

Retrieving a Java Object with JPA

• Hibernate/JPA CRUD (5)

// retrieve/read from database using the primary key
// in this example, retrieve Student with primary key: 1

Student myStudent = entityManager.find(Student.class, 1);

Development Process

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

Step 1: Add new method to DAO interface

public interface StudentDAO {  
	...
	
    Student findById(Integer id);  
    
}

Step 2: Define DAO implementation

Step 3: Update main app

@SpringBootApplication  
public class CruddemoApplication {  
  
   public static void main(String[] args) {  
      SpringApplication.run(CruddemoApplication.class, args);  
   }  
  
   @Bean  
   public CommandLineRunner commandLineRunner(StudentDAO studentDAO){  
      return runner-> {  
      // createStudent(studentDAO);  
         readStudent(studentDAO);  
      };  
   }  
  
   private void readStudent(StudentDAO studentDAO) {  
  
      // create a student object  
      System.out.println("Creating new student object...");  
      Student tempStudent = new Student("Daffy","Duck", "@daffy@gmail.com");  
  
      // save the student  
      System.out.println("Saving the student...");  
      studentDAO.save(tempStudent);  
  
      // display id of the saved student  
      int theId = tempStudent.getId();  
      System.out.println("Saved student. Generated id: " + theId);  
  
      // retrieve student based on the id: primary key  
      System.out.println("Retrieving student with id: " + theId);  
      Student myStudent = studentDAO.findById(theId);  
  
      // display student  
      System.out.println("Found the student: " + myStudent);  
  
  
   }  
  ....
}