What Good is a Flexible Paperclip?

Jon Yurek

Originally found at http://flickr.com/photos/toofarnorth/9984261

Since it’s the Holidays, I’ve been spending a bit more time than normal on Paperclip. And since that time has been particularly fruitful and there’s been a release or two, I figured I should probably tell someone about it before I friggin’ explode. It’s all about making Paperclip more flexible, more adaptable, and more friendly to use. Can you believe there’s more to file uploads than avatars?

Newer, more sensible defaults

Overall, this is actually a bit small on the change meter, but it may affect some of you, so it’s up front. The :path and :url defaults have changed. By default now, files will be saved to :rails_root/public/system/:attachments/:id/:style/:basename/:extension. It’s the system part of that that’s important, because now it means that if you’re deploying with Capistrano, you don’t have to do anything and your attachments will survive deployments. This was not previously the case, regrettably, but it is now!

Callbacks and such

Thanks to the callback methods pioneered by ActiveRecord itself with the fantastic before_save and family, Paperclip now defines a before_post_process and after_post_process callback, which can be used exactly like all the AR callbacks. Not only that, if you’re the kind of person who likes to have more than one attachment on a model, there are per-attachment callbacks as well, called before_<attachment>_post_process and after_<attachment>_post_process. The before_ callbacks are fully capable of stopping processing if they need to, simply by returning false (not nil, but false, which is a distinction ActiveRecord makes, as well). Thus, if you are uploading images that have E in the name, you can write a before_post_process that looks like this:

class User < ActiveRecord::Base
  has_attached_file :avatar, :styles => {:tiny => "32x32#" }
  before_post_process :check_avatar_name_for_capital_e

  def check_avatar_name_for_capital_e
    not self.avatar.original_filename.match(/E/)

This will prevent the image from being thumbnailed. It will not prevent the attachment from being saved, though. Just from being processed. As a bonus, something else that will prevent attachments from being processed is failing validation. If you have a size, content_type, or presence validation that fails, the attachment will not go through processing (which means ImageMagick won’t try to convert that Word Doc into a PNG if you don’t want it to).

Expanded Post-Processing

I realize that there’s more to image uploads than thumbnailing. And there’s more to file uploads than images. But until now, all you could do was thumbnail your images. What gives! Well, starting now you can define your own processors that can do whatever you want to your uploads. You can:

  • add rounded corners
  • invert
  • rotate
  • OCR
  • pick out every third word of your text docs
  • run spellcheck
  • automatically print them out

… well, you can if you can write code, since none of those exist yet. The only one that’s written is still the thumbnailer/format converter.

But the point is that now you can have Paperclip do whatever you want. Check out the Paperclip::Processor class documentation for more info on exactly what you need to do to make a Processor, but the gist is that you’ll take in a file and some options, and you spit back out a file. That’s pretty much it, and Paperclip places no limits on what you can do, say, or call during that time (so if you spend 30 seconds rendering a POVRay scene, that’s your fault for making your users wait).

Paperclip will automatically detect files in your Rails app’s lib/paperclip_processors directory, so just drop them there and you’ll be running in no time.

The Code

As always, the code is available for forking and cloning on GitHub, and the documentation is available on our site.

If you’d like to contribute to paperclip with a patch, bug report, or feature request, don’t hesitate to get on over to the Paperclip Google group, or our Paperclip Lighthouse. As much as we like GitHub, we don’t really work well with pull requests from there. Creating a LH ticket with a link to the branch you want us to pull works much better.

Visit our Open Source page to learn more about our team’s contributions.