protected void btn_Submit_Add_Click(object sender, EventArgs e)
        {
            Bookstore_BO bookstorebo = new Bookstore_BO();
            int          ProductId   = Convert.ToInt32(TB_ID_Add.Text);

            bookstorebo.retrieveProduct(ProductId);

            Product prodObj = bookstorebo.retrieveProduct(ProductId);

            if (prodObj != null)
            {
                TB_Error_Add.Text    = "Product already exist, consider updating instead";
                TB_Error_Add.Visible = true;
            }
            else
            {
                {
                    int count = 0;
                    //validate file upload
                    string filename;
                    if (FileUploadImage.HasFile)
                    {
                        string extension = System.IO.Path.GetExtension(FileUploadImage.FileName);
                        if (extension == ".jpg" || extension == ".png")
                        {
                            filename = FileUploadImage.FileName;
                            FileUploadImage.PostedFile.SaveAs(Server.MapPath("~/Image/") + filename);
                            string ImageURL = "~/Image/" + filename;
                            lbl_Image_Name.Text = ImageURL;
                            //codes to send to BO
                        }
                        else
                        {
                            sb.AppendLine("File has to be .jpg or .png only");
                            count++;
                        }
                    }
                    else
                    {
                        sb.AppendLine("Please upload an image");
                        count++;
                    }

                    //validate ID Textbox
                    if (TB_ID_Add.Text.Trim() == "")
                    {
                        sb.AppendLine("Please indicate product ID");
                        count++;
                    }
                    else if (System.Text.RegularExpressions.Regex.IsMatch(TB_ID_Update.Text, " ^ [0-9]"))
                    {
                        sb.AppendLine("Please enter valid product ID");
                        count++;
                    }

                    //validate Name Textbox
                    if (TB_Name_Add.Text.Trim() == "")
                    {
                        sb.AppendLine("Please indicate product name");
                        count++;
                    }

                    //validate Price Textbox
                    if (TB_Price_Add.Text.Trim() == "" || TB_Price_Add.Text.All(Char.IsLetter))
                    {
                        sb.AppendLine("Please amend product price");
                        count++;
                    }

                    //validate Education DDL
                    if (Ddl_Edu_Add.SelectedItem.Text == "~Education Level~")
                    {
                        sb.AppendLine("Please indicate Education Level of product");
                        count++;
                    }

                    //validate Item DDL
                    if (Ddl_Item_Add.SelectedItem.Text == "~Item Type~")
                    {
                        sb.AppendLine("Please indicate product type");
                        count++;
                    }

                    //validate Quantity
                    if (TB_Quantity_Add.Text == "")
                    {
                        sb.AppendLine("Please enter available quantity of product");
                        count++;
                    }

                    if (count > 0)
                    {
                        lbl_Message.Text     = "";
                        TB_Error_Add.Visible = true;
                        TB_Error_Add.Text    = sb.ToString();
                    }
                    else
                    {
                        //codes to send to database

                        bookstorebo.uploadProduct(TB_ID_Add.Text, lbl_Image_Name.Text, TB_Name_Add.Text, Convert.ToDouble(TB_Price_Add.Text), Ddl_Edu_Add.SelectedItem.Text, Ddl_Item_Add.SelectedItem.Text, Convert.ToInt32(TB_Quantity_Add.Text), lbl_Any.Text, lbl_AnyType.Text);
                        FileUploadImage.Attributes.Clear();
                        TB_ID_Add.Text             = "";
                        TB_Name_Add.Text           = "";
                        TB_Price_Add.Text          = "";
                        Ddl_Edu_Add.SelectedIndex  = -1;
                        Ddl_Item_Add.SelectedIndex = -1;
                        TB_Quantity_Add.Text       = "";
                        lbl_Message.Visible        = true;
                        lbl_Message.Text           = "Product has been added successfully!";
                        TB_Error_Add.Text          = "";
                        TB_Error_Add.Visible       = false;
                    }
                }
            }
        }