/// <summary>
        /// Select tat ca hang hoa trong kho
        /// </summary>
        /// <returns></returns>
        public Entities.ChiTietKhoHang[] SelectAll()
        {
            List<Entities.ChiTietKhoHang> arrC = new List<ChiTietKhoHang>();
            try
            {
                string sql = "";
                sql = "Select b.MaKho, b.MaHangHoa, a.TenHangHoa, b.NgayNhap,b.HanSuDung,b.SoLuong,b.GhiChu from HangHoa a join ChiTietKhoHang b on a.MaHangHoa=b.MaHangHoa where b.Deleted='false'";
                conn = new Connection();
                cn = conn.openConnection();
                cmd = new SqlCommand(sql, cn);
                dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                while (dr.Read())
                {
                    Entities.ChiTietKhoHang ctkho = new Entities.ChiTietKhoHang();
                    ctkho.MaKho = dr["MaKho"].ToString();
                    ctkho.MaHangHoa = dr["MaHangHoa"].ToString();
                    ctkho.TenHangHoa = dr["TenHangHoa"].ToString();
                    ctkho.SoLuong = Convert.ToInt32(dr["SoLuong"].ToString());
                    ctkho.NgayNhap = DateTime.Parse(dr["NgayNhap"].ToString());
                    ctkho.HanSuDung = DateTime.Parse(dr["HanSuDung"].ToString());
                    ctkho.GhiChu = dr["GhiChu"].ToString();
                    arrC.Add(ctkho);
                }
            }

            catch (Exception ex)
            {
                string s = ex.Message.ToString();
            }
            finally
            {
                cmd.Connection.Dispose();
                cn.Close();
                conn.closeConnection();
            }

            return arrC.ToArray();
        }