使用會話和查詢字符串進行參數化

Question

我正面臨一條錯誤消息，但我不知道行中的sql語句的原因：

DACatPgeVIPLIST.Fill(dsCatPgeVIPLIST);

它顯示此消息，您可以幫我嗎：

參數化查詢(@Country nvarchar(7),@Category nvarchar(4000))SELECT a.[AdsID],期望未提供參數@Category 。

碼：

if (Session["location"] != null)
{
    using (SqlConnection CatPgeVIPLISTsqlCON = new SqlConnection(cs))
    {
        CatPgeVIPLISTsqlCON.Open();

        SqlDataAdapter DACatPgeVIPLIST = new SqlDataAdapter("SELECT a.[AdsID], a.[Country], a.[State], a.[City], a.[AdsTit], SUBSTRING(a.[AdsDesc], 1, 70) as AdsDesc, a.[AdsPrice], a.[Img1] FROM [ads] as a INNER JOIN [UserInfo] as u on u.UID = a.UID WHERE a.[Country] = @Country and a.[Category] = @Category and u.VIP = 'Yes'", cs);

        string location = Convert.ToString(Session["location"]);
        string category = Request.QueryString["category"];

        DACatPgeVIPLIST.SelectCommand.Parameters.AddWithValue("@Country", location);
        DACatPgeVIPLIST.SelectCommand.Parameters.AddWithValue("@Category", category);

        DataSet dsCatPgeVIPLIST = new DataSet();

        DACatPgeVIPLIST.Fill(dsCatPgeVIPLIST);

        CatPgeVIPLIST.DataSource = dsCatPgeVIPLIST.Tables[0];
        CatPgeVIPLIST.DataBind();
    }
}

Answer 1

以下代碼行可能會將null分配給類別：

string category = Request.QueryString["category"];

您可能會這樣解決，它將null轉換為空字符串：

string category = Convert.ToString(Request.QueryString["category"]);

或者，您可以嘗試傳遞DBNull.Value而不是null （未經測試）：

DACatPgeVIPLIST.SelectCommand.Parameters
               .AddWithValue("@Category", (object)category ?? DBNull.Value);