public bool XoaNhanVien(string MaNV, ref string error)
        {
            try
            {
                QuanLyCaPheEntities qlcp = new QuanLyCaPheEntities();

                ChamCong chamcong = new ChamCong();
                chamcong.MaNV = int.Parse(MaNV);

                qlcp.ChamCongs.Attach(chamcong);
                qlcp.ChamCongs.Remove(chamcong);

                qlcp.SaveChanges();

                return(true);
            }
            catch (Exception err)
            {
                error = err.Message;
                return(false);
            }
        }
        public bool ThemNhanVien(string MaNV, string TenNV, ref string error)
        {
            try
            {
                QuanLyCaPheEntities qlcp = new QuanLyCaPheEntities();

                ChamCong chamcong = new ChamCong();

                chamcong.MaNV   = int.Parse(MaNV);
                chamcong.TenNV  = TenNV;
                chamcong.GioIn  = TimeSpan.Zero;
                chamcong.GioOut = TimeSpan.Zero;

                qlcp.ChamCongs.Add(chamcong);
                qlcp.SaveChanges();

                return(true);
            }
            catch (Exception err)
            {
                error = err.Message;
                return(false);
            }
        }