I need help to figure out how to store the document in the database.
The DB storage needs to be a BLOB (or the equivalent) since you want to store an arbitrary number of types of 'things' of presumably arbitrary size. There is a resource out there on the web, somewhere (if I could recall where, the link would be yours, but I seem to recall muddling through it with attachment_fu, so you might want to check those references).
I did that personally as a proof of concept in my app about a year ago, but found the DB storage and retrieval much, much too slow as compared to the file system.
