C＃

Question

我在另一个数据阅读器中打开一个数据阅读器，但是当我打开第二个数据阅读器并尝试读取数据时，它表示即使我刚打开它也会关闭它。

这是我的功能：

protected void checkBookStockAgain()
    {
        SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionStore"].ConnectionString);
        conn.Open();
        string selectCartString = "Select Item, Price, Quantity From ShoppingCart Where Username = @User";
        SqlCommand cmd = new SqlCommand(selectCartString, conn);
        cmd.Parameters.AddWithValue("@User", Session["user"].ToString());
        SqlDataReader readCart = cmd.ExecuteReader();
        while (readCart.Read())
        {
            string selectBookInfo = "Select Quantity from BookInfo where Title = @Title";
            SqlCommand bookInfoQuantitycmd = new SqlCommand(selectBookInfo, conn);
            bookInfoQuantitycmd.Parameters.AddWithValue("@Title", readCart["Item"]);
            SqlDataReader quantityReader = bookInfoQuantitycmd.ExecuteReader();
            while (quantityReader.Read())
            {
                if (Convert.ToInt32(readCart["Quantity"]) > Convert.ToInt32(quantityReader["Quantity"]))
                {
                    updateCart = false;
                    quantityReader.Close();
                    readCart.Close();
                    conn.Close();
                }
                else if (Convert.ToInt32(readCart["Quantity"]) < Convert.ToInt32(quantityReader["Quantity"]))
                {
                    updateCart = true;
                    invQuantity = Convert.ToInt32(quantityReader["Quantity"].ToString()) - Convert.ToInt32(readCart["Quantity"].ToString());
                    quantityReader.Close();
                    readCart.Close();
                    conn.Close();
                }
                else if (Convert.ToInt32(readCart["Quantity"]) == Convert.ToInt32(quantityReader["Quantity"]))
                {
                    updateCart = true;
                    removeBookFromStore(readCart);
                    quantityReader.Close();
                    readCart.Close();
                    conn.Close();
                }
                else
                {
                    quantityReader.Close();
                    readCart.Close();
                    conn.Close();
                }
            }
        }
    }

给出的错误指出“读取器关闭时无效尝试调用读取”，并且尝试通过quantityReader运行while循环时发生错误。作为旁注，我在连接字符串中启用了MARS（多个活动结果集）。