protected void OnDDListSelectionChanged_Click(object sender, EventArgs e)
        {
            ProductController productController = new ProductController();
            CategoryController categoryController = new CategoryController();

            string category = ((DropDownList)sender).SelectedItem.Text;
            dgProducts.DataSourceID = null;

            if (!string.IsNullOrEmpty(category))
            {
                dgProducts.DataSource = productController.SelectByCategoryId(
                                        categoryController.GetIdByName(category));
            }

            dgProducts.DataBind();
        }