无法从数据库下载文件

Question

I've inherited this site and having issues with file downloads. Files such as .pdf, .doxs, .txt are saved in Sql as image. A datalist controls is used with a a href controls to view it/downloaded it but it's not working. And I realize that a href control is not a proper control to use but not sure what control to use.

Here is the aspx markup:

<asp:DataList ID="DataList2" runat="server" DataSourceID="SqlDataSource2" DataKeyField="fileId">
   <ItemTemplate>
     <a href='<%# "~/UserControls/FileFetch.ashx?fileId=" + Convert.ToString(Eval("fileId")) %>' target="_blank">
       <%# Convert.ToString(Eval("fileName"))%></a>
   </ItemTemplate>
</asp:DataList>
<asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:ClubSiteDB %>"
  SelectCommand="SELECT [fileId], [fileName], [postedBy] FROM [FilesLibrary]">                
</asp:SqlDataSource>

A helper file called FileFetch.ashx is used to get the file:

<%@ WebHandler Language="C#" Class="FileFetch" %>

using System;
using System.Web;
using System.Data.SqlClient;
using System.Data;
using System.IO;

public class FileFetch : IHttpHandler
{
    const int BUFFERSIZE = 1024;

    public bool IsReusable
    {
       get
       {
           return true;
       }
    }

    public void ProcessRequest(HttpContext context)
    {
       HttpResponse response = context.Response;
       HttpRequest request = context.Request;
       response.ContentType = "response.ContentType";
       response.Cache.SetCacheability(HttpCacheability.Public);
       response.BufferOutput = false;
       writeSingleImage(Convert.ToInt32(request.QueryString["fileId"]), response.OutputStream);
       response.End();
    }

    public void writeSingleImage(int fileId, Stream output)
    {
        string cxnstr = System.Configuration.ConfigurationManager.ConnectionStrings["ClubSiteDB"].ConnectionString;
        SqlConnection connection = new SqlConnection(cxnstr);
        string query;
        query = "SELECT fileData FROM dbo.FilesLibrary where fileId=@fileId";

        SqlCommand command = new SqlCommand(query, connection);
        SqlParameter param0 = new SqlParameter("@fileId", SqlDbType.Int);
        param0.Value = fileId;
        command.Parameters.Add(param0);
        connection.Open();

        byte[] d = ((byte[])(command.ExecuteScalar()));
        output.Write(d, 0, d.Length);
        connection.Close();
   }

}

Answer 1

I'm going to take a stab at this and say you need to change your Anchor tag to be the following:

<a href='<%# Page.ResolveUrl("~/UserControls/FileFetch.ashx?fileId=" + Convert.ToString(Eval("fileId"))) %>' target="_blank">

The MSDN link to the Page.ResolveUrl method is here . Page inherits from Control, hence why the link refers to Control.ResolveUrl.

I've just seen that another alternative is to add runat="server" to the Anchor tag to turn it into a server control.