How to set file privileges based on database users

I need to create an html based file manager (in rails) with just basic functions (download, delete, upload) used by groups of clients/developers.

1. (How) Can i set a file to just b开发者_开发知识库e shown (readable) to a group of users (stored in database) only?
2. Is it an option to store the whole files (binary) in the database? Won't it create huge db?
3. Is there any way to solve this somehow with just directories?

1. http://boxroom.rubyforge.org/ is doing exactly what you describe. It is open source, so you might want to have a look at how they did.

2. Yes. Yes but you might judge it acceptable depending on the amount of data.

3. Yes. Coding that is possible.