public void DeleteTrainee(string id)
        {
            Trainee trainee_t = new Trainee();

            if (Trainee_by_id(id) == false)
            {
                throw new Exception("Trainee " + id + " not exist");
            }



            XElement trainee_XElement;

            try
            {
                trainee_XElement = (from stu in XMLDS.Trainees.Elements()
                                    where stu.Element("id").Value == id
                                    select stu).FirstOrDefault();
                trainee_XElement.Remove();
                XMLDS.SaveTrainees();
            }
            catch
            {
            }
        }
        public void AddTrainee(Trainee t)
        {
            bool flag = true;

            flag = Tester_by_id(t.Id);
            if (flag == true)
            {
                throw new Exception("Tester " + t.Id + " is Already exist!!");
            }


            flag = Trainee_by_id(t.Id);
            if (flag == true)
            {
                throw new Exception("There is a trinee with id: " + t.Id + " is Already exist!!");
            }

            try
            {
                //Create a new trinee path
                XElement id        = new XElement("id", t.Id);
                XElement firstName = new XElement("firstName", t.Name);
                XElement lastName  = new XElement("lastName", t.FamilyName);
                XElement name      = new XElement("name", firstName, lastName);
                XElement BIRTH_DAY = new XElement("BIRTH_DAY", t.BrithDate);
                XElement City      = new XElement("City", t.MyAddress.city);
                XElement Street    = new XElement("Street", t.MyAddress.streetName);
                XElement Number    = new XElement("Number", t.MyAddress.houseNumber);
                XElement Address   = new XElement("Address", City, Street, Number);

                XElement Gear     = new XElement("Gear", t.MyGear);
                XElement Gender   = new XElement("Gender", t.MyGender);
                XElement Type_car = new XElement("Type_car", t.MyGear);
                XElement Teacher  = new XElement("Teacher", t.TeacherName);
                XElement LESSONS  = new XElement("LESSONS", t.NumberOfLessons);
                XElement SCHOOL   = new XElement("SCHOOL", t.School);
                //  XElement PhonePrefix = new XElement("phone_number", t.PhonePrefix);
                XElement phone_number = new XElement("phone_number", t.PhoneNumber);
                XElement Password     = new XElement("Password", t.Password);
                XMLDS.Trainees.Add(new XElement("student", id, name, BIRTH_DAY, Address, Gear, Gender, Type_car, Teacher, LESSONS, SCHOOL, phone_number, Password));
                XMLDS.SaveTrainees();
            }
            catch
            {
                throw new Exception("Can't open trinees file");
            }
        }
        public void UpdateTrainee(Trainee t)
        {
            try
            {
                //Trainess_Root = XMLDS.Trainees;
            }
            catch (Exception)
            {
            }
            Trainee trainee_t = new Trainee();

            try
            {
                XElement traineeElement = (from stu in XMLDS.Trainees.Elements()
                                           where (stu.Element("id").Value) == t.Id
                                           select stu).FirstOrDefault();
                traineeElement.Element("BIRTH_DAY").Value    = t.BrithDate.ToString();
                traineeElement.Element("Gender").Value       = t.MyGender.ToString();
                traineeElement.Element("Type_car").Value     = t.Car.ToString();
                traineeElement.Element("Teacher").Value      = t.TeacherName.ToString();
                traineeElement.Element("LESSONS").Value      = t.NumberOfLessons.ToString();
                traineeElement.Element("SCHOOL").Value       = t.School;
                traineeElement.Element("phone_number").Value = t.PhoneNumber;
                traineeElement.Element("Gear").Value         = t.MyGear.ToString();
                traineeElement.Element("Password").Value     = t.Password;
                traineeElement.Element("name").Element("firstName").Value = t.Name;
                traineeElement.Element("name").Element("lastName").Value  = t.FamilyName;
                traineeElement.Element("Address").Element("City").Value   = t.MyAddress.city;
                traineeElement.Element("Address").Element("Street").Value = t.MyAddress.streetName;
                traineeElement.Element("Address").Element("Number").Value = t.MyAddress.houseNumber.ToString();
                XMLDS.SaveTrainees();
            }
            catch (Exception Ex)
            {
                throw new Exception(Ex.ToString());
            }
        }