Curious about new (ActiveRecord::Base)

Because the documentation isn’t clear (at least to me)…

I have a Logfile model that has corresponding fields in MySql.
The main ones are id, fileName, and content type. However, I can pass a
File object to a new Logfile and have handlers that I created in the
Logfile class extract the data. However, the documentation states
“…you canâ??t have attributes that arenâ??t part of the table columns.”
Why is this possible (this isn’t really a problem, but I just wanted to
know)?

The above method works for individual files.

My problem is this - I would like to have rubyzip exctract files to
create new Logfiles. My current method is to iterate through the
ZipFile using foreach, but this yields ZipEntries. Is there a way to
extract this as a Tempfile until its final destination is determined
using my above-mentioned handlers? Or is there a better way to go about
this?

Please point me to the proper docs and I’ll do my best to figure it out.
Thank you!