شرح علاقة One-to-Many بالتفصيل

• الـ name لازم يكون unique = true - ما بنحتاج قسمين بنفس الاسم
• الـ nullable = false - اسم القسم إلزامي دائماً

بعد ما تضيف الـ Annotation @Entity، Spring Boot ينشئ جدول department تلقائياً. تأكد إنك حاطط ddl-auto=create وبعدين ارجع لـ none.

Repository والـ Service

رح ننشئ نفس الطبقات اللي عملناها للـ Employee:

@Repository
public interface DepartmentRepository extends JpaRepository<Department, UUID> {
}

public interface DepartmentService {
    List<Department> findAll();
    Department findOne(UUID departmentId);
    Department create(Department department);
    void deleteOne(UUID departmentId);
}

Service Implementation

@Service
public class DepartmentServiceImpl implements DepartmentService {

    @Autowired
    private DepartmentRepository departmentRepository;

    @Override
    public List<Department> findAll() {
        return departmentRepository.findAll();
    }

    @Override
    public Department findOne(UUID departmentId) {
        return departmentRepository.findById(departmentId)
            .orElseThrow(() -> CustomResponseException.resourceNotFound(
                "Department with ID " + departmentId + " not found"
            ));
    }

    @Override
    public Department create(Department department) {
        return departmentRepository.save(department);
    }

    @Override
    public void deleteOne(UUID departmentId) {
        Department department = findOne(departmentId);
        departmentRepository.deleteById(department.getId());
    }
}

Controller

@RestController
@RequestMapping("/departments")
public class DepartmentController {

    private final DepartmentService departmentService;

    public DepartmentController(DepartmentService departmentService) {
        this.departmentService = departmentService;
    }

    @GetMapping
    public ResponseEntity<GlobalResponse<List<Department>>> findAll() {
        return new ResponseEntity<>(
            new GlobalResponse<>(departmentService.findAll()), HttpStatus.OK
        );
    }

    @PostMapping
    public ResponseEntity<GlobalResponse<Department>> create(
            @RequestBody Department department) {
        return new ResponseEntity<>(
            new GlobalResponse<>(departmentService.create(department)), HttpStatus.CREATED
        );
    }

    @DeleteMapping("/{departmentId}")
    public ResponseEntity<Void> delete(@PathVariable UUID departmentId) {
        departmentService.deleteOne(departmentId);
        return new ResponseEntity<>(HttpStatus.NO_CONTENT);
    }
}

ربط Employee بالـ Department

بعد ما أنشأنا الـ Department Entity والجدول تاعتها، لازم نربطها مع الـ Employee.

بالـ Employee Entity، بنستبدل departmentId بعلاقة حقيقية:

@Entity
@Table(name = "employee")
public class Employee {
    // ... باقي الخصائص

    @ManyToOne
    @JoinColumn(name = "department_id", nullable = true)
    private Department department;
}

• @ManyToOne - يعني كثير Employees لـ Department واحد
• @JoinColumn(name = "department_id") - يحدد اسم العمود اللي فيه الـ Foreign Key

الـ Department من ناحية الـ Employee

بالعلاقة One-to-Many:

• الـ Employee يعرف عنده @ManyToOne - كثير موظفين لقسم واحد
• الـ Department ممكن يعرف @OneToMany للوصول لموظفيه

@Entity
@Table(name = "department")
public class Department {
    @Id
    @GeneratedValue
    @UuidGenerator
    private UUID id;

    @Column(name = "name", nullable = false, unique = true)
    private String name;

    @OneToMany(mappedBy = "department")
    private List<Employee> employees;
}

الـ mappedBy = "department" يشير لاسم الـ Field بالـ Employee اللي يمثل العلاقة.

الخلاصة

بالدرس الجاي رح نكمل على علاقات ثانية مثل Leave Requests.