從WebForms中的查詢中獲取指定值

Question

我在從查詢中獲取指定值時遇到問題。 我的GridView收到一行，但是當我嘗試讀取該值以將其放入某個變量時，它說我沒有任何值。

else if (Request.QueryString.AllKeys.Contains("a"))
{
    String sql_user = "SELECT c1.ID, c1.SHORT_NAME, ao1.NAME, c1.REGON FROM (tabel1 c1 LEFT JOIN tabel2 ao1 ON c1.ID = ao1.ID WHERE c1.ID = ?";
    connection.OPEN();

    OleDbCommand sql_s = new OleDbCommand(sql_user, polaczenie);

    sql_s.Parameters.add("?", OleDbType.Integer).Value = Request.QueryString["a"];

    OleDbDataAdapter sqlDa = new OleDbDataAdapter(sql_s);

    DataTable dt = new DataTable();
    sqlDa.Fill(dt);

    GRID_VIEW1.DataSource = dt;

    GRID_VIEW1.DataBind();

    OleDbDataReader customer = sql_s.ExecuteReader();

    // i want to get SHORT_NAME so that one below i think dosent work

    // but any way it make me an Exception of any value not found but on GridView it shows me clearly one ROW
    learerLabel.Text = (String) cmd.ExecuteScalar();

    connection.Close();
}

我以許多方式（例如“會話”或“閱讀器”）來執行此操作，但是我現在不放棄所有嘗試，但始終會說我的查詢沒有任何價值。 我究竟做錯了什么？ 謝謝

Answer 1

嘗試此操作，將參數名稱替換為@ID，有關傳遞參數的msdn文檔，請參見下面的鏈接

SELECT c1.ID, c1.SHORT_NAME, ao1.NAME, c1.REGON FROM (tabel1 c1 LEFT JOIN tabel2 ao1 ON c1.ID = ao1.ID WHERE c1.ID = @ID
sql_s.Parameters.add("@ID", OleDbType.Integer).Value = Request.QueryString["a"];

下面的msdn https://msdn.microsoft.com/zh-cn/library/bbw6zyha(v=vs.110).aspx中提供了有關傳遞參數的更多詳細信息。

Answer 2

更好的方法是：

    public class MyClass
{
    public int Id { get; set; }
    public string ShortName { get; set; }
    public string Name { get; set; }
    public int Regon { get; set; }
}

接下來，要從查詢中獲取數據，請嘗試以下操作：

            CustomClass item = new CustomClass();

        String sql_user = "SELECT c1.ID, c1.SHORT_NAME, ao1.NAME, c1.REGON FROM (tabel1 c1 LEFT JOIN tabel2 ao1 ON c1.ID = ao1.ID WHERE c1.ID = @id";

        using (var conn = new OleDbConnection("connectionString"))
        {
            conn.Open();
            using (var cmd = new OleDbCommand(sql_user, conn))
            {
                cmd.Parameters.Add("@id", OleDbType.Integer).Value = Request.QueryString["a"];
                cmd.Prepare();

                var reader = cmd.ExecuteReader();

                if(reader.Read())
                {
                    item.Id = (int)reader["ID"];
                    item.ShortName = reader["SHORT_NAME"].ToString();
                    item.Name= reader["NAME"].ToString();
                    item.Regon = (int)reader["REGON"];
                }
                conn.Close();
            }

        }

編輯：如果您不想使用它，則需要更改行：

OleDbDataReader customer = sql_s.ExecuteReader();

至：

            OleDbDataReader customer;
        var dr = sql_s.ExecuteReader();

        if (dr.Read())
            customer = dr;

試試這個，並把它寫工作