public static function validateStudentId($studentId)
{
if (!preg_match("/^[0-9]{6,7}\$/", $studentId)) {
throw new Exception("Student id can contain only numbers of length 6 to 7");
}
if (StudentFetcher::existsStudentId($studentId)) {
throw new Exception("Student id entered already exists in database.");
// the array of errors messages
}
}
