C# – How to cache images from a SQl Server 2005 database call

asp.netccachingsql-server-2005

I am having trouble using the output cache param in an aspnet 2.0 page directive. I am using a session variable to hold the value of the selected image. It seems that the dynamic control in a datalist, is not working when the output cache is set to true in the page directive. Is there a way to cache the images seperately to avoid using a page directive?

datalist code

" RepeatColumns="6" CellPadding="8" CellSpacing="8" GridLines="Both" SelectedItemStyle-BackColor="#33ff66" OnSelectedIndexChanged="dtlImages_SelectedIndexChanged" OnItemCommand="dtlImages_ItemCommand">

' Runat="server">

' ID="lblDescription" Font-Bold="True" Font-Size="12px" Font-Names="Arial">

code that retrieves the image from the database

protected void Page_Load(object sender, System.EventArgs e)
{
string strImageID = Request.QueryString["id"];

        string wf4uConnect = System.Configuration.ConfigurationManager.ConnectionStrings["wf4uConnectionString"].ConnectionString;
        System.Data.SqlClient.SqlConnection wf4uConn = new System.Data.SqlClient.SqlConnection(wf4uConnect);

        System.Data.SqlClient.SqlCommand myCommand = new SqlCommand("Select ImageFile, ImageType from wf4u_ImageThumb Where ImageId =" + strImageID, wf4uConn);

        wf4uConn.Open();

        SqlDataReader byteReader = myCommand.ExecuteReader(CommandBehavior.CloseConnection);

        while ((byteReader.Read())) 
        { 
            Response.BinaryWrite((byte [])byteReader.GetValue(0)); 
            Response.ContentType = (string)byteReader.GetValue(1); 
        }

        wf4uConn.Close(); 
    }

I have implemented an http context object to cache the images as they're loaded into the webpage.

public ImageList (string clientName)
{
HttpContext context = HttpContext.Current;

        if((context.Cache["ImageIdList" + clientName] == null))
        {
            string wf4uConnect = System.Configuration.ConfigurationManager.ConnectionStrings["wf4uConnectionString"].ConnectionString;
            System.Data.SqlClient.SqlConnection wf4uConn = new System.Data.SqlClient.SqlConnection(wf4uConnect);
            string queryStr = "SELECT ImageId FROM wf4u_imageThumb WHERE ClientName = @ClientName";
            SqlCommand ImageIdComm = new System.Data.SqlClient.SqlCommand(queryStr, wf4uConn);
            ImageIdComm.Parameters.Add("@ClientName", SqlDbType.VarChar).Value = clientName;

            wf4uConn.Open();

            SqlDataReader ImageIdReader = ImageIdComm.ExecuteReader();

            if (ImageIdReader.Read())
            {
                _ImageId = ImageIdReader.GetInt32(0);
                _ClientName = ImageIdReader.GetString(1);

                context.Cache.Insert("ImageIdList" + clientName, this, null, DateTime.Now.AddSeconds(600), TimeSpan.Zero);
            }

            wf4uConn.Close();
        }
        else
        {
            ImageList list = (ImageList)context.Cache["ImageIdList" + clientName];

            _ImageId = list.ImageId;
            _ClientName = list.ClientName;
        }
    }

any suggestions would be welcomed.

Best Answer

You can implement an async handler like this:

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

public class FileHandler : IHttpAsyncHandler
{
    #region Variables
    private HttpContext _currentContext = null;

    protected SqlCommand _command = null;
    protected delegate void DoNothingDelegate();
    #endregion

    public void ProcessRequest(HttpContext context)
    {
    }

    public void DoNothing()
    {
    }

    public bool IsReusable
    {
        get { return false; }
    }

    #region IHttpAsyncHandler Members
    public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
    {

        _currentContext = context;

        int imageId;
        if (int.TryParse(context.Request.QueryString["imageId"], out imageId))
        {
            // begin get file - make you own
            // return FileController.BeginGetFile(out _command, cb, extraData, imageId);
        }
        else
        {
            DoNothingDelegate doNothingDelegate = new DoNothingDelegate(DoNothing);

            return doNothingDelegate.BeginInvoke(cb, extraData);
        }
    }

    public void EndProcessRequest(IAsyncResult result)
    {
        File file = null;
        if (null != _command)
        {
            try
            {   
                // end get file - make your own
                // file = FileController.EndGetFile(_command, result);
            }
            catch { }
        }

        if (null != file)
        {
            // in my case File entity may be stored as a binary data
            //or as an URL
            // here is URL processing - redirect only
            if (null == file.Data)
            {
                _currentContext.Response.Redirect(file.Path);
            }
            else
            {
                _currentContext.Response.ContentType = file.ContentType;
                _currentContext.Response.BinaryWrite(file.Data);
                _currentContext.Response.AddHeader("content-disposition", "filename=\"" + file.Name + (file.Name.Contains(file.Extension) ? string.Empty : file.Extension) + "\"" );
                _currentContext.Response.AddHeader("content-length", (file.Data == null ? "0" : file.Data.Length.ToString()));

            }

            _currentContext.Response.Cache.SetCacheability(HttpCacheability.Private);
            _currentContext.Response.Cache.SetExpires(DateTime.Now);
            _currentContext.Response.Cache.SetSlidingExpiration(false);
            _currentContext.Response.Cache.SetValidUntilExpires(false);
                        _currentContext.Response.Flush();
        }
        else
        {
            throw new HttpException(404, HttpContext.GetGlobalResourceObject("Image", "NotFound") as string);
        }
    }
    #endregion
}

And set necessary values to the cache headers.

EDIT: Guess, in this case it would be better to use headers instead of using Cache object.

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