I'd like to be able to read an XML file uploaded by the user (less than 100kb), but not have to first save that file to the database. I don't need that file past the current action (its contents get parsed and added to the database; however, parsing the file is not the problem). Since local files can be read with:

File.read("export.opml")

I thought about just creating a file_field for :uploaded_file, then trying to read it with

File.read(params[:uploaded_file])

but all that does is throw a TypeError (can't convert HashWithIndifferentAccess into String). I really have tried a lot of various things (including reading from the /tmp directory as well), but could get none of them to work.

I hope the brevity of my question doesn't mask the effort I've given to try to solve this on my own, but I didn't want to pollute this question with a hundred ways of how NOT to get it done. Big thanks to anyone who chimes in.