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Getting and Displaying Images from SQL Server with C#

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Now that Jesse Smith has taught you how to store those system-taxing images in your SQL Server database, you do rather need to know how to get them back out again when the user accesses a page. C# comes to the rescue with easy scripts for grab-and-display.
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In part 1 of this series, I explained how to use C# scripts to get your web site's images into your SQL Server database. In this article, I show you how to win the second half of the battle by retrieving images from SQL Server and displaying them in a web page.

Getting and displaying an image with C# is actually considerably easier than putting the image into SQL Server. Basically, all we do is write the image's binary stream to the web page. And here's a bonus: The scripts not only display the images, but resize them! This technique is great for eCommerce sites; you can show thumbnails for product images; the thumbnail blows up into the full-size image only when the user clicks the thumbnail.

Streaming the Images

Listing 1 shows the code-behind script (.cs) for image streaming to a web page.

Listing 1 The code-behind script for displaying the image

1 using System;
2 using System.Drawing;
3 using System.Drawing.Imaging;
4 using System.IO;
5 using System.Data;
6 using System.Data.SqlClient;

7 namespace ImageResizing {

8 public class MainDisplay : System.Web.UI.Page {

9 public void Page_Load(System.Object sender, System.EventArgs e) {

10 try {

11 System.Int32 _ImgID = System.Convert.ToInt32(Request.QueryString["ImgID"]);

12 System.Int32 _height = System.Convert.ToInt32(Request.QueryString["height"]);

13 System.Int32 _width = System.Convert.ToInt32(Request.QueryString["width"]);

14 System.Data.SqlClient.SqlConnection Con = new System.Data.SqlClient.SqlConnection( "Data Source=;database=e-commerce;uid=webappsx;pwd=tyqldf" );

15 System.String SqlCmd = "SELECT * FROM Image WHERE img_pk = @ImageID";

16 System.Data.SqlClient.SqlCommand SqlCmdObj = new System.Data.SqlClient.SqlCommand( SqlCmd, Con );

17 SqlCmdObj.Parameters.Add("@ImageID", System.Data.SqlDbType.Int).Value = _ImgID;

18 Con.Open();

19 System.Data.SqlClient.SqlDataReader SqlReader = SqlCmdObj.ExecuteReader();

20 SqlReader.Read();

21 System.Web.HttpContext.Current.Response.ContentType = "image/jpeg";

22 System.Drawing.Image _image = System.Drawing.Image.FromStream( new System.IO.MemoryStream( (byte[])SqlReader["img_data"] ) );

23 System.Drawing.Image _newimage = _image.GetThumbnailImage( _width, _height, null, new System.IntPtr() );

24_newimage.Save( System.Web.HttpContext.Current.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg );

26 } catch (System.Exception Ex) {

27 System.Web.HttpContext.Current.Trace.Write(Ex.Message.ToString());

28 }

29 }

30 }

31 }

Lines 1–6 of Listing 1 load our namespaces from the .NET library. Line 2 loads the System.Drawing namespace that's needed for displaying and resizing images to scale. The other namespaces are straightforward; they're for streaming binary data (System.IO namespace on line 4) and SQL Server objects (lines 5–6).

Line 7 starts the ImageResizing namespace; it contains a single class called MainDisplay that does all the work of retrieving and displaying the image. This class contains the C# Page_Load function that tells the script compiler that this code is to be executed every time the page is loaded or refreshed.

On lines 11–13 we get the ID, height, and width of the image to be displayed. As you'll see in the next section, we tell this script what these parameters are from the calling web page script.

Next, we set up and open an SQL Server connection to a database called e-commerce and perform a query against a table called Image based on the ID of the image we want to display. After setting up a data reader to index into the recordset of this table, on line 21 we tell the script compiler that the image will be of type JPEG or GIF, the most popular image formats for the web.

Lines 22–24 use the nifty System.Drawing namespace functions. Line 22 looks a bit confusing because it has nested function calls. It sets up a new class type called _image that's derived from the Image class type of the System.Drawing namespace. The _image type consists of a new memory stream that's created by a class called System.IO.MemoryStream, passed to the FromStream function of the Image class. We pass the System.IO.MemoryStream class the data from the img_data field of the Image table, as a byte array. Byte arrays are often used to store binary (image) data for formatting and efficiency reasons.

On line 23, we create yet another new class type, called newimage, derived from the _image class type we just created, and instantiate a method called GetThumbnailImage. This method is passed the width and height of the main image we'll display, and scales the image to the specified size. The IntPtr function is also passed to this method (with no value).

Finally, and most importantly, we use the Save method of the Image class type to retrieve the image output stream from the HTTP protocol and save it as a .jpg image when it reaches the browser.

Save this script with any name you like. For this example, I'll call it imagegen.aspx.cs.

Now it's time to look at the web page script that calls on the code-behind script above. Adding the ability to load images to a web page is easy and the same code-behind script can be used every time.

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