public void FillStudents()
        {
            List <Student> students = studentDTO.GetAll();

            foreach (Student item in students)
            {
                dgvStudents.Rows.Add(
                    item.Id,
                    item.Firstname,
                    item.Lastname,
                    item.Group.Name,
                    item.Group.Classroom.Name
                    );
            }
        }