The Art of SQL Server FILESTREAM - Red Gate Software

Chapter 5: FILESTREAM with ASP.NET and SilverlightLab 8: Using SqlFileStream in an N-Tier ScenarioFor many reasons, today's web applications are often architected to run across multiplephysical computers, referred to as tiers. Using FILESTREAM in a multi-tier designrequires attention to an important detail: in order to achieve the most benefit fromFILESTREAM, it should be accessed using the Win32 streaming APIs. However, usingSqlFileStream also requires an active transaction in the SQL Server database. Theconsumer of the FILESTREAM data is most often the tier closest to the client – andfurthest away from the database. If the SqlFileStream API is used, this requires thatthis tier has at least some knowledge of the data store. In general, this violates goodarchitectural practices.In this lab, we will create a solution that makes the presentation tier as independent onthis database transaction as possible, while maintaining the performance benefits offeredby streaming access to FILESTREAM data. To fully understand the problem involved, let'sconsider the following example scenario. A web application must handle requests fromclients for which the response includes data stored in a SQL Server FILESTREAM column.The web application will be hosted on a front-end IIS web server, while the SQL Serverdatabase is hosted on a back-end server. The web application's developers aim to makethe application as efficient as possible, and want to use the SqlFileStream classand copy the stream's contents to the Response object's OutputStream (as shown inListing 5-11 as part of Lab 6). They have four options, as shown below.• Start the SqlTransaction required for the SqlFileStream to use in thepresentation tier.This solution requires that the web application has intimate knowledge of thedatabase's configuration and details. Generally, one of the architectural goals of amulti-layered web application is to avoid this.• Start a SqlTransaction and create the SqlFileStream in the data access layerand pass the SqlFileStream back to the client application.This solution does not address the concern that the SqlTransaction must be activewhile the presentation layer uses the SqlFileStream object. The client, however, has204