ruby on rails - Smarter paperclip validations

Question

I'm using paperclip in a rails app and have the following three validations in my model

validates_attachment_presence :photo                    
validates_attachment_size :photo, :less_than=>1.megabyte
validates_attachment_content_type :photo, :content_type=>['image/jpeg', 'image/png', 'image/gif'] 

If the user forgets to add an attachment, all three validations fail and thus, the user is presented with the following three errors:

# Photo file name must be set.
# Photo file size file size must be between 0 and 1048576 bytes.
# Photo content type is not included in the list

I think it would be best to just show the first error in this instance since the other two errors are purely consequential... I would prefer the user to only ever see the second two errors if an attachment has been added but doesn't meet the validation criteria.

I'm certain there is no pre-baked validation that does this sort of thing and from reading the code in vendor/plugins/paperclip/lib/paperclip.rb I see that the validates_attachment_size method supports the :unless parameter as shown:

def validates_attachment_presence name, options = {}
  message = options[:message] || "must be set."
  validates_presence_of :"#{name}_file_name", 
                        :message => message,
                        :if      => options[:if],
                        :unless  => options[:unless]
end

So, I was thinking that I could do something like the following:

validates_attachment_size :photo, :less_than=>1.megabyte, :unless=> :photo.blank

But that breaks the app. Anyone have any experience of doing this sort of thing? Would be a nice contribution to the paperclip source code.

EDIT:

I've tried using this:

validates_attachment_size :photo, :less_than=>1.megabyte, 
     :unless=> Proc.new { |image| image[:photo].nil? }

It doesn't quite work though as I've just managed to upload a 5mb mp3 with this validation in place. But it's promising as the error message doesn't appear when the user has not attached a photo.

Answer 1

validates_attachment_size :photo, :less_than => 1.megabyte, 
  :unless => Proc.new { |imports| imports.photo_file_name.blank? }