thoughtbot/paperclip — pull request #1272 by jyurek (2013-07-01 23:56:43+00:00)
Title: Validate the attachment before we attach without calling valid?

OK, let's try this one on for size again.

From the commit:
Using the ActiveRecord validations is smart in order to lessen load on
the project to develop our own validators, but it's problematic in that
calling `valid?` on the record fires off all the other validations --
including those on fields which may not be set yet because of
mass-assignment. This commit will "pre-validate" the attachment's fields
so that it doesn't process an invalid attachment, but it does so by
running its validations manually on assignment.