public List<ProductAttr> GetAttrsByCategoryID(string categoryid)
        {
            var dal = new ProductsDAL();
            DataTable dt = dal.GetAttrsByCategoryID(categoryid);

            List<ProductAttr> list = new List<ProductAttr>();
            foreach (DataRow dr in dt.Rows)
            {
                ProductAttr model = new ProductAttr();
                model.FillData(dr);
                list.Add(model);
            }
            return list;
        }