Paperclip

Paperclip is intended as an easy file attachment library for ActiveRecord. The intent behind it was to keep setup as easy as possible and to treat files as much like other attributes as possible. This means they aren't saved to their final locations on disk, nor are they deleted if set to nil, until ActiveRecord::Base#save is called. It manages validations based on size and presence, if required. It can transform its assigned image into thumbnails if needed, and the prerequisites are as simple as installing ImageMagick (which, for most modern Unix-based systems, is as easy as installing the right packages). Attached files are saved to the filesystem and referenced in the browser by an easily understandable specification, which has sensible and useful defaults.

See the documentation for has_attached_file in Paperclip::ClassMethods for more detailed options.

The complete RDoc is online.

Requirements

ImageMagick must be installed and Paperclip must have access to it. To ensure that it does, on your command line, run which convert (one of the ImageMagick utilities). This will give you the path where that utility is installed. For example, it might return /usr/local/bin/convert.

Then, in your environment config file, let Paperclip know to look there by adding that directory to its path.

In development mode, you might add this line to config/environments/development.rb):

Paperclip.options[:command_path] = "/usr/local/bin/"

If you're on Mac OSX, you'll want to run the following with Homebrew:

brew install imagemagick

If you are dealing with pdf uploads or running the test suite, also run:

brew install gs

Installation

Paperclip is distributed as a gem, which is how it should be used in your app. It's technically still installable as a plugin, but that's discouraged, as Rails plays well with gems.

Include the gem in your Gemfile:

gem "paperclip", "~> 2.4"

Or, if you don't use Bundler (though you probably should, even in Rails 2), with config.gem

# In config/environment.rb
...
Rails::Initializer.run do |config|
  ...
  config.gem "paperclip", :version => "~> 2.4"
  ...
end

For Non-Rails usage:

class ModuleName < ActiveRecord::Base
    include Paperclip::Glue
    ...
end

Quick Start

In your model:

class User < ActiveRecord::Base
  has_attached_file :avatar, :styles => { :medium => "300x300>", :thumb => "100x100>" }
end

In your migrations:

class AddAvatarColumnsToUser < ActiveRecord::Migration
  def self.up
    add_column :users, :avatar_file_name,    :string
    add_column :users, :avatar_content_type, :string
    add_column :users, :avatar_file_size,    :integer
    add_column :users, :avatar_updated_at,   :datetime
  end

  def self.down
    remove_column :users, :avatar_file_name
    remove_column :users, :avatar_content_type
    remove_column :users, :avatar_file_size
    remove_column :users, :avatar_updated_at
  end
end

In your edit and new views:

<%= form_for :user, @user, :url => user_path, :html => { :multipart => true } do |form| %>
  <%= form.file_field :avatar %>
<% end %>

In your controller:

def create
  @user = User.create( params[:user] )
end

In your show view:

<%= image_tag @user.avatar.url %>
<%= image_tag @user.avatar.url(:medium) %>
<%= image_tag @user.avatar.url(:thumb) %>

To detach a file, simply set the attribute to nil:

@user.avatar = nil
@user.save

Usage

The basics of paperclip are quite simple: Declare that your model has an attachment with the has_attached_file method, and give it a name. Paperclip will wrap up up to four attributes (all prefixed with that attachment's name, so you can have multiple attachments per model if you wish) and give them a friendly front end. The attributes are <attachment>_file_name, <attachment>_file_size, <attachment>_content_type, and <attachment>_updated_at. Only <attachment>_file_name is required for paperclip to operate. More information about the options to has_attached_file is available in the documentation of Paperclip::ClassMethods.

Attachments can be validated with Paperclip's validation methods, validates_attachment_presence, validates_attachment_content_type, and validates_attachment_size.

Storage

The files that are assigned as attachments are, by default, placed in the directory specified by the :path option to has_attached_file. By default, this location is ":rails_root/public/system/:attachment/:id/:style/:filename". This location was chosen because on standard Capistrano deployments, the public/system directory is symlinked to the app's shared directory, meaning it will survive between deployments. For example, using that :path, you may have a file at

/data/myapp/releases/20081229172410/public/system/avatars/13/small/my_pic.png

NOTE: This is a change from previous versions of Paperclip, but is overall a safer choice for the default file store.

You may also choose to store your files using Amazon's S3 service. You can find more information about S3 storage at the description for Paperclip::Storage::S3.

Files on the local filesystem (and in the Rails app's public directory) will be available to the internet at large. If you require access control, it's possible to place your files in a different location. You will need to change both the :path and :url options in order to make sure the files are unavailable to the public. Both :path and :url allow the same set of interpolated variables.

Post Processing

Paperclip supports an extensible selection of post-processors. When you define a set of styles for an attachment, by default it is expected that those "styles" are actually "thumbnails". However, you can do much more than just thumbnail images. By defining a subclass of Paperclip::Processor, you can perform any processing you want on the files that are attached. Any file in your Rails app's lib/paperclip_processors directory is automatically loaded by paperclip, allowing you to easily define custom processors. You can specify a processor with the :processors option to has_attached_file:

has_attached_file :scan, :styles => { :text => { :quality => :better } },
                         :processors => [:ocr]

This would load the hypothetical class Paperclip::Ocr, which would have the hash "{ :quality => :better }" passed to it along with the uploaded file. For more information about defining processors, see Paperclip::Processor.

The default processor is Paperclip::Thumbnail. For backwards compatability reasons, you can pass a single geometry string or an array containing a geometry and a format, which the file will be converted to, like so:

has_attached_file :avatar, :styles => { :thumb => ["32x32#", :png] }

This will convert the "thumb" style to a 32x32 square in png format, regardless of what was uploaded. If the format is not specified, it is kept the same (i.e. jpgs will remain jpgs).

Multiple processors can be specified, and they will be invoked in the order they are defined in the :processors array. Each successive processor will be given the result of the previous processor's execution. All processors will receive the same parameters, which are what you define in the :styles hash. For example, assuming we had this definition:

has_attached_file :scan, :styles => { :text => { :quality => :better } },
                         :processors => [:rotator, :ocr]

then both the :rotator processor and the :ocr processor would receive the options "{ :quality => :better }". This parameter may not mean anything to one or more or the processors, and they are expected to ignore it.

NOTE: Because processors operate by turning the original attachment into the styles, no processors will be run if there are no styles defined.

If you're interested in caching your thumbnail's width, height and size in the database, take a look at the paperclip-meta gem.

Also, if you're interested in generating the thumbnail on-the-fly, you might want to look into the attachment_on_the_fly gem.

Events

Before and after the Post Processing step, Paperclip calls back to the model with a few callbacks, allowing the model to change or cancel the processing step. The callbacks are before_post_process and after_post_process (which are called before and after the processing of each attachment), and the attachment-specific before_<attachment>_post_process and after_<attachment>_post_process. The callbacks are intended to be as close to normal ActiveRecord callbacks as possible, so if you return false (specifically

returning nil is not the same) in a before_ filter, the post processing step will halt. Returning false in an after_ filter will not halt anything, but you can access the model and the attachment if necessary.

NOTE: Post processing will not even start if the attachment is not valid according to the validations. Your callbacks and processors will only be called with valid attachments.

URI Obfuscation

Paperclip has an interpolation called :hash for obfuscating filenames of publicly-available files.

Example Usage:

has_attached_file :avatar, {
    :url => "/system/:hash.:extension",
    :hash_secret => "longSecretString"
}

The :hash interpolation will be replaced with a unique hash made up of whatever is specified in :hash_data. The default value for :hash_data is ":class/:attachment/:id/:style/:updated_at".

:hash_secret is required, an exception will be raised if :hash is used without :hash_secret present.

For more on this feature read the author's own explanation. https://github.com/thoughtbot/paperclip/pull/416

MD5 Checksum / Fingerprint

A MD5 checksum of the original file assigned will be placed in the model if it has an attribute named fingerprint. Following the user model migration example above, the migration would look like the following.

class AddAvatarFingerprintColumnToUser < ActiveRecord::Migration
  def self.up
    add_column :users, :avatar_fingerprint, :string
  end

  def self.down
    remove_column :users, :avatar_fingerprint
  end
end

Custom Attachment Processors

Custom attachment processors can be implemented and their only requirement is to inherit from Paperclip::Processor (see lib/paperclip/processor.rb). For example, when :styles are specified for an image attachment, the thumbnail processor (see lib/paperclip/thumbnail.rb) is loaded without having to specify it as a :processor parameter to has_attached_file. When any other processor is defined it must be called out in the :processors parameter if it is to be applied to the attachment. The thumbnail processor uses the imagemagick convert command to do the work of resizing image thumbnails. It would be easy to create a custom processor that watermarks an image using imagemagick's composite command. Following the implementation pattern of the thumbnail processor would be a way to implement a watermark processor. All kinds of attachment processors can be created; a few utility examples would be compression and encryption processors.

Dynamic Configuration

Callable objects (lambdas, Procs) can be used in a number of places for dynamic configuration throughout Paperclip. This strategy exists in a number of components of the library but is most significant in the possibilities for allowing custom styles and processors to be applied for specific model instances, rather than applying defined styles and processors across all instances.

Dynamic Styles:

Imagine a user model that had different styles based on the role of the user. Perhaps some users are bosses (e.g. a User model instance responds to #boss?) and merit a bigger avatar thumbnail than regular users. The configuration to determine what style parameters are to be used based on the user role might look as follows where a boss will receive a 300x300 thumbnail otherwise a 100x100 thumbnail will be created.

class User < ActiveRecord::Base
  has_attached_file :avatar, :styles => lambda { |attachment| { :thumb => (attachment.instance.boss? ? "300x300>" : "100x100>") }
end

Dynamic Processors:

Another contrived example is a user model that is aware of which file processors should be applied to it (beyond the implied thumbnail processor invoked when :styles are defined). Perhaps we have a watermark processor available and it is only used on the avatars of certain models. The configuration for this might be where the instance is queried for which processors should be applied to it. Presumably some users might return [:thumbnail, :watermark] for its processors, where a defined watermark processor is invoked after the thumbnail processor already defined by Paperclip.

class User < ActiveRecord::Base
  has_attached_file :avatar, :processors => lambda { |instance| instance.processors }
  attr_accessor :watermark
end

Deploy

Paperclip is aware of new attachment styles you have added in previous deploy. The only thing you should do after each deployment is to call rake paperclip:refresh:missing_styles. It will store current attachment styles in RAILS_ROOT/public/system/paperclip_attachments.yml by default. You can change it by:

Paperclip.registered_attachments_styles_path = '/tmp/config/paperclip_attachments.yml'

Here is an example for Capistrano:

namespace :deploy do
  desc "build missing paperclip styles"
  task :build_missing_paperclip_styles, :roles => :app do
    run "cd #{release_path}; RAILS_ENV=production bundle exec rake paperclip:refresh:missing_styles"
  end
end

after("deploy:update_code", "deploy:build_missing_paperclip_styles")

Now you don't have to remember to refresh thumbnails in production everytime you add new style. Unfortunately it does not work with dynamic styles - it just ignores them.

If you already have working app and don't want rake paperclip:refresh:missing_styles to refresh old pictures, you need to tell Paperclip about existing styles. Simply create paperclip_attachments.yml file by hand. For example:

class User < ActiveRecord::Base
  has_attached_file :avatar, :styles => {:thumb => 'x100', :croppable => '600x600>', :big => '1000x1000>'}
end

class Book < ActiveRecord::Base
  has_attached_file :cover, :styles => {:small => 'x100', :large => '1000x1000>'}
  has_attached_file :sample, :styles => {:thumb => 'x100'}
end

Then in RAILS_ROOT/public/system/paperclip_attachments.yml:

---
:User:
  :avatar:
  - :thumb
  - :croppable
  - :big
:Book:
  :cover:
  - :small
  - :large
  :sample:
  - :thumb

Testing

Paperclip provides rspec-compatible matchers for testing attachments. See the documentation on Paperclip::Shoulda::Matchers for more information.

Contributing

If you'd like to contribute a feature or bugfix: Thanks! To make sure your fix/feature has a high chance of being included, please read the following guidelines:

Ask on the mailing list[http://groups.google.com/group/paperclip-plugin], or post a new GitHub Issue[http://github.com/thoughtbot/paperclip/issues].
Make sure there are tests! We will not accept any patch that is not tested. It's a rare time when explicit tests aren't needed. If you have questions about writing tests for paperclip, please ask the mailing list.

Please see CONTRIBUTING.md for details.

Credits

Paperclip is maintained and funded by thoughtbot, inc

Thank you to all the contributors!

The names and logos for thoughtbot are trademarks of thoughtbot, inc.