public IHttpActionResult Add([FromBody]SINHVIEN st)
 {
     using (QLSVEntities db = new QLSVEntities())
     {
         db.SINHVIENs.Add(st);
         db.SaveChanges();
         return Ok();
     }
 }
 public IHttpActionResult Delete([FromBody]string mssv)
 {
     using (QLSVEntities db = new QLSVEntities())
     {
         SINHVIEN sv = (from s in db.SINHVIENs where s.MSSV == mssv select s).First();
         db.SINHVIENs.Remove(sv);
         db.SaveChanges();
         return Ok();
     }
 }
        public IHttpActionResult Update([FromBody]SINHVIEN news_sv)
        {
            using (QLSVEntities db = new QLSVEntities())
            {
                SINHVIEN sv = (from s in db.SINHVIENs where s.MSSV == news_sv.MSSV select s).First();
                sv.HOTEN = news_sv.HOTEN;
                sv.KHOA = news_sv.KHOA;
                sv.NGANH = news_sv.NGANH;
                sv.DIACHI = news_sv.DIACHI;
                sv.SDT = news_sv.SDT;

                db.SaveChanges();
                return Ok();
            }
        }