How to use the File Attachment Module with a legacy database

The File Attachments Module provides the capability to easily implement a file upload and download functionality in your application. However, the built-in FileData class is persistent, and thus requires a separate table in the database to store file contents and names. Moreover, with XPO model, the built-in FileData class stores file contents in compressed form. These specifics make this class useless for XAF applications that must work with a legacy database. It is quite typical for a legacy database that a file is stored in a BLOB field of the table with other fields of the same object and in a plain form. Also, the same reecord may contain multiple BLOB fields for different files. To handle this and other various scenarios, a non-persistent class that implements the IFileData interface can be created.

This example demonstrates a possible IFileData implementation in a non-persistent class that actually passes data to and from the owner persistent XPO object, where the BLOB (byte[]) property is declared.

Important notes:
- Since the IFileData implementor class is non-persisent, the object space cannot create its instances. So, we create the only instance in the persistent class constructor.
- The IFileData property must have a setter to allow uploading files in ASP.NET.
- In this example, the file name is not stored in the object, but generated from the object key value. It is only used when the file is downloaded by the client.