datatable添加新列问题

Question

我想添加一个新列url代码如下：
aspx.cs：
string strcon = "Data Source=localhost; Initial Catalog=Netshop; Integrated Security=SSPI";
 public DataTable excuteselect(string sqlstr)
        {
            SqlConnection conn=new SqlConnection(strcon);
            conn.Open();
            SqlCommand cmd=new SqlCommand();
            cmd.Connection=conn;
            cmd.CommandText=sqlstr;
            SqlDataAdapter sda=new SqlDataAdapter();
            sda.SelectCommand=cmd;
            DataSet ds=new DataSet();
            sda.Fill(ds,"tb_goodsinfo");
            return ds.Tables["tb_goodsinfo"];
        }
protected void Page_Load(object sender, EventArgs e)
        {
                string sqlstr = "select [goodsid],[goodsname],[goodsprice],[goodsphoto],[goodstypename] from tb_goodsinfo join tb_goodstype on tb_goodsinfo.goodstypeid=tb_goodstype.goodstypeid where tb_goodsinfo.goodstypeid='" + Request.QueryString["typeid"].ToString() + "';";
                DataTable dt = new DataTable();
                dt = excuteselect(sqlstr);
                DataColumn columnurl = new DataColumn("url");
                dt.Columns.Add(columnurl);
                columnurl.Caption = "url";
                columnurl.ColumnName = "url";
                foreach (DataRow drrow in dt.Rows)
                {
                    drrow["url"] = "goodsdetails.aspx?id=" + drrow["goodsid"].ToString();
                } 
                dlsortshow.DataSource = dt.DefaultView;
                dlsortshow.DataBind();
        }
 aspx：  
  <asp:DataList ID="dlsortshow" runat="server" Width="850px" RepeatDirection="Horizontal" RepeatColumns="3">
      <ItemTemplate>
        &nbsp;&nbsp;&nbsp;&nbsp;<asp:ImageButton ID="ibtphoto" runat="server" Width="218px" Height="230px" ImageUrl='<%#Eval("goodsphoto") %>'/>&nbsp;&nbsp;&nbsp;&nbsp;<br />
        <asp:LinkButton ID="lbtname" runat="server" Text='<%#Eval("goodsname") %>' PostBackUrl='<%#Eval("url") %>'></asp:LinkButton><br />
        售价：￥<asp:Label ID="lbprice" runat="server" Text='<%#Eval("goodsprice") %>'></asp:Label><br /><br />
      </ItemTemplate>
    </asp:DataList>  运行结果显示：DataBinding:“System.Data.DataRowView”不包含名为“url”的属性。 
也就是意味着添加新列没有成功，请问该怎样添加这一新列url呢

Answer 1

 dt.Columns.Add("url",typeof(string));

Answer 2

要先创建schema然后再填充数据。