Image files are a standard part of every ASP.NET
application. While most sites use Web server directories to store image files,
another option is utilizing a database. The database provides a better approach
to managing application image files. In this article, we examine using SQL
Server 2000 to manage image files with ASP.NET via both VB.NET and C#.
Using a database for image management may not be appropriate
for smaller applications with images that rarely (if ever) change, but it is an
excellent option for an application that contains numerous images that may
frequently change. Also, additional information may be stored with the image to
facilitate searching, sorting, and so forth.
The key to storing images in a database is the actual
backend data store. In this article, we use a SQL Server 2000 table that
contains identity, name, description, content type, file size, and image
fields. The name and description columns are text. The identity column is
numeric and the image data type is used for the actual image. The content type
field is text and file size is integer, with these two fields used to display
the image. The T-SQL in
creates the table. In addition, we’ll use a stored procedure to actually place images into the table. View
Listing B. We utilize this stored procedure via our VB.NET and C# code
to populate the table.
Placing images in the database
The first step in the process is inserting the images into
the SQL Server database. This may be simplified (for the user) by providing a
Web user interface. We can easily provide this interface via ASP.NET. The C# code in
Listing C provides a simple
interface, allowing the user to enter a description for the image and the
actual image file via an HTML input field (System.Web.UI.HtmlControls.HtmlInputFile
object). This allows the user to browse the file system and submit an
image. (Listing D contains the equivalent VB.NET code.)
A few notes about this code:
HTML input field <input type=file> allows the user to select the
necessary image file (which will be inserted into the database). The PostedFile property of this control provides access to
the submitted file. An HttpPostedFile object is
used to work with the submitted file.
encoding type of the form is set to multipart/form-data (enctype=”multipart/form-data”) to facilitate
the submission of the image file.
label control is used to notify the user of any errors processing a
submission. It is located at the top of the page, and it is only visible
and contains text if an exception is encountered.
- The System.Data and System.Data.SqlClient
namespaces are utilized to work with the backend database.
- The System.IO namespace is necessary for working with the
stream to save the image.
- SqlParameter objects are used to submit values for the
stored procedure parameters.
name associated with an image (Name field in database table) is populated
via the filename property of the uploaded file. In addition, the content
type and file size are retrieved from the uploaded file.
cleanup is handled in the finally block.
Using the stored images
At this point, users may add image files to the database, so
we can use these images in an application. The content type and file size
stored with the image are used to spit the image to the screen (or wherever it
is needed). The C# code in
retrieves an image from the database and displays it via the Response
object. (Listing F contains the VB.NET equivalent code.)
A few notes about the code:
image id is hard-coded, but we could easily pass a value into the page via
retrieved from the database are cast to the necessary values for the
Response object is used to spit out the image stored in the database. The
image is read and written as a byte stream using the Write method of the
Response object’s OutputStream property.
Just the beginning
Using a database as a vehicle for image storage and
organization provides a much cleaner solution than using the standard file
system. Next week, we’ll take the concept further by enhancing the
administration interface and offering a better approach to using the images on
an ASP.NET powered site.
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