HQL mapping example

different files

Course.java:

...
@Entity
@Table(name = "courses")
public class Course {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String title;

    @ManyToMany(mappedBy = "courses") // связь с Student через маппинг
    private List<Student> students;

   ...
}

=====================================================================================

Student.java:

...
@Entity
@Table(name = "students")
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    private String email;

    @ManyToMany // связь с Course через маппинг
    @JoinTable(
            name = "student_courses",
            joinColumns = @JoinColumn(name = "student_id"),
            inverseJoinColumns = @JoinColumn(name = "course_id")
    )
    private List<Course> courses;
    
    ...
}

=====================================================================================

StudentService.java:

...
@Service
public class StudentService {

    @Autowired
    private StudentRepo studentRepository;

    @PersistenceContext
    private EntityManager entityManager;

    // HQL-запрос: получение всех курсов для студента по ID
    @Transactional(readOnly = true)
    public List<Course> findCoursesByStudentId(Long studentId) {
        String hql = "SELECT s.courses FROM Student s WHERE s.id = :studentId"; // использование маппинга
        return entityManager.createQuery(hql, Course.class)
                .setParameter("studentId", studentId)
                .getResultList();
    }

    // HQL-запрос: получение всех студентов, записанных на курс
    @Transactional(readOnly = true)
    public List<Student> findStudentsByCourseTitle(String courseTitle) {
        String hql = "SELECT s FROM Student s JOIN s.courses c WHERE c.title = :courseTitle"; // использование маппинга
        return entityManager.createQuery(hql, Student.class)
                .setParameter("courseTitle", courseTitle)
                .getResultList();
    }

    // HQL-запрос: добавление курса для студента
    @Transactional
    public void addCourseToStudent(Long studentId, Long courseId) {
        Student student = studentRepository.findById(studentId)
                .orElseThrow(() -> new EntityNotFoundException("Студент с ID " + studentId + " не найден"));
        Course course = entityManager.find(Course.class, courseId);
        if (course == null) {
            throw new EntityNotFoundException("Курс с ID " + courseId + " не найден");
        }
        student.getCourses().add(course); // использование маппинга для добавления курса
        studentRepository.save(student);
    }
}