如何通过Spring data统计OneToMany元素的项数

@Entity
public class Parent {
    @Id
    private Long id;
    
    @OneToMany(mappedBy = "parent")
    private List<Child> children;
    
    // getters and setters
}

@Entity
public class Child {
    @Id
    private Long id;
    
    @ManyToOne
    private Parent parent;
    
    // getters and setters
}

public interface ParentRepository extends JpaRepository<Parent, Long> {
    @Query("SELECT COUNT(c) FROM Parent p JOIN p.children c WHERE p.id = :parentId")
    Long countChildrenByParentId(@Param("parentId") Long parentId);
}

@Service
public class ParentService {
    @Autowired
    private ParentRepository parentRepository;
    
    public Long countChildrenByParentId(Long parentId) {
        return parentRepository.countChildrenByParentId(parentId);
    }
}