For one of the projects I am working on these days, I had to provide image hosting from the database meaning the images will be stored in the the database when the user uploads them to my site and is fetched from the database on request. After looking around for hardly 15mins the solution was there. SQL Server's image type came to the rescue but I read in some article that MS was going to discontinue this type and only keep the varbinary for such purposes. While its available in SQL Server 2005, why not take advantage of it.
Let's say we have the following table structure which represents the different sites of an organization. Each site has its own logo and needs to be displayed on different pages of our site.
Let's first look at how to save the image in the database when it is uploaded from one of the pages in the website (in case its desktop application there is one less step here).
If this were a desktop application I would have probably written:
Let me explain the code here a little. The fuLogoImage is a FileUpload control and the code is simply checking if a file was uploaded through the control when the pages was submitted, using its HasFile property. If it was, then simply get the file as a byte[] and use ADO.Net to write this array to a Image column in the database. In my case here I have used a Typed Dataset, hence the "ta" before the Sites representing the TableAdapter for the Sites table. Notice I simply passed the byte[] without any additional work. You can also simply write a Insert command with the byte[] placed at the right column and ADO.Net will take care of the streaming to database.
Once the file is stored in the database in the LogoImage column, we can then start writing code to display it in our pages. Since the images are being generated dynamically for a given ID, we need a method to bypass the static URL requirement of the image tag. Luckily, there is such a trick and it is called a HTTP Handler. Everything you service in a web server is handled through an HTTP handler, including your aspx pages. If you go to IIS Manager and open the properties of any application, then open the configuration tab, you will see a window like this:
which shows the handler for each type of file the web server (IIS) will be dealing with. Basically, IIS itself does not know how to deal with a file so it passes on the handing responsibility to one of these programs depending on the extension. If I double click the aspx handler description, I see:
So, all http commands for the aspx file are being handled by the asp_isapi.dll extension. This extension is responsible for all the aspx page interpretation, session handling and other features that you like so much. Coming back to our topic, we need to write a handler just like that to generate images dynamically. For that we will use the ASP.Net generic http handler. If you go to your project and add new item, you will see:
Adding this will give you something like this:
The handler implements the IHttpHandler interface which has the capability to handle all the Http commands like Get and Post etc. I you would like session handing capabilities then you can also implement the IRequiresSessionState or IReadOnlySessionState interface. Now, the IHttpHandler contains a function called ProcessRequest where we need to implement our custom logic. I am passing the image ID as a query string parameter to the handler and the code looks like the following:
public void ProcessRequest (HttpContext context)
{
byte[] image;
context.Response.ContentType = "image/jpeg";
decimal siteid = decimal.Parse(context.Request.QueryString["SiteID"]);
if (siteid == -1)
image = GetNoLogo(context);
else
{
ECFormsTableAdapters.Lkp_SitesTableAdapter taSites = new ECFormsTableAdapters.Lkp_SitesTableAdapter();
ECForms.Lkp_SitesDataTable dtSites = taSites.GetDataBySiteID(siteid);
if (dtSites.Count == 0 || dtSites[0].LogoImage == null)
image = GetNoLogo(context);
else
image = dtSites[0].LogoImage;
}
context.Response.BinaryWrite(image);
}Here I fetch the image from the database and then simply write it to the response stream using the proper content type description. In my example I have placed the limit that the image has to be a jpg, as visible from the content type header. The GetNoLogo function basically replaces the image with a default logo that is stored in the file system. The code looks something like this:
private byte[] GetNoLogo(HttpContext context)
{
byte[] imageNoLogo;
string nologopath = context.Server.MapPath("images/nologo.jpg");
lock (lockObject)
{
FileStream fs = new FileStream(nologopath, FileMode.Open,FileAccess.Read);
imageNoLogo = new byte[fs.Length];
fs.Read(imageNoLogo, 0, (int)fs.Length);
fs.Close();
}
return imageNoLogo;
}I have put a lock around the file access to prevent multiple threads from simultaneously opening the file. I should use some caching strategy here but for the moment it is good enough. Now to use it in the asp.net code I define a image tag anywhere in the html
<asp:Image ID="ImgLogo" runat="server" Height="52px" />
and make the src look like this through the code in Page_Load:
ImgLogo.ImageUrl = string.Format("ImageHandler.ashx?SiteID={0}", SelectedSite);and that's it! When the browser renders this image it calls the associated url for image and at the web server this url is a handler that dynamically renders the image using the parameter. Create a site with dynamic images from the database now. Obvious advantages include:
- Single storage of all files.
- Centralized management
- Database searching and meta data storage facility for the images
- Centralized backup and recovery
Some disadvantages include:
- Performance hit
- Single point of failure
But then, the choice is yours. Depending on the situation you have to pick one over another.
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