File creation transaction in DocumentController

[Hjorthen]

Currently files are stored before registering them in the database. It is possible to create a transaction, which makes sure that the database is consistent with the file system.

• Write file to temp folder
• Retrieve unique file name
• Write unique name to database under a transaction
• Move file to unique name from temp folder
• Commit transaction

The only way that the store can become in an inconsistent state is if the commit of the transaction fails. A scheduling thread could periodically scan files in the file system and remove those which have no entry in the database.