I was working lately on a Sinatra project, and got fascinated on how fast you can get things up and running. Everything was beautiful, until I tried to upload a file using paperclip. Although Paperclip was originally built for rails [Ken Robertson](http://invalidlogic.com/dm-paperclip/) ported it to Datamapper. Let me explain in few steps how you can upload with Paperclip, using Datamapper. Start declaring your model like this:

class Resource
  include DataMapper::Resource
  include Paperclip::Resource

  property :id,     Serial

  has_attached_file :file,
                    :url => "/system/:attachment/:id/:style/:basename.:extension",
                    :path => "#{APP_ROOT}/public/system/:attachment/:id/:style/:basename.:extension"
end

You'll need to specify your :url and :path options as the ones built into dm-paperclip are merb centric which won't quite work. Also set APP_ROOT to where ever your application root directory with your static Sinatra folder is. Now your routes should look something like this:

post '/upload' do
  resource = Resource.new(:file => make_paperclip_mash(params[:file]))
  halt "There were some errors processing your request..." unless resource.save
end

And there's the tricky part, on the **make_paperclip_mash** method. Paperclip expects the file object loaded from the form to be in a different form than what is created by default. To fix this you should create a Mash (which is just a Hash, unless you're actually using merb):

def make_paperclip_mash(file_hash)
  mash = Mash.new
  mash['tempfile'] = file_hash[:tempfile]
  mash['filename'] = file_hash[:filename]
  mash['content_type'] = file_hash[:type]
  mash['size'] = file_hash[:tempfile].size
  mash
end

And that's it, now you can upload files using Paperclip right on your Sinatra app with Datamapper. You can check out the code of this example at: [sinatra_paperclip.rb](http://gist.github.com/291877)

While developing an application with Sebastián that allow users to upload videos with some file name restrictions, meaning that it must contain only A-Z and 0-9 digits, underscores (_) as a valid component as well, and also the name must be preceded by it's own #id, we came up with the need of applying this custom filter to each uploaded video. After doing some research on paperclip source code and internet tutorials, we suggest the following solution:

class Video < ActiveRecord::Base
  has_attached_file :video,
    :path => ":rails_root/public/system/:attachment/:id/:style/:normalized_video_file_name",
    :url => "/system/:attachment/:id/:style/:normalized_video_file_name"

  Paperclip.interpolates :normalized_video_file_name do |attachment, style|
    attachment.instance.normalized_video_file_name
  end

  def normalized_video_file_name
    "#{self.id}-#{self.video_file_name.gsub( /[^a-zA-Z0-9_\.]/, '_')}"
  end
end

What are we doing here? Easy, in **has_attached_file** we edit the way paperclip returns the **path** and **url** by default, the most relevant components when saving and loading the file in order to display it. Paperclip default values are:

path default => ":rails_root/public/system/:attachment/:id/:style/:filename"
url default => "/system/:attachment/:id/:style/:filename"

Values preceded by ':' are the standard interpolations paperclip has. For further information on this visit [http://wiki.github.com/thoughtbot/paperclip/interpolations(Interpolations)](http://wiki.github.com/thoughtbot/paperclip/interpolations.) What we did was change **:filename** with **:normalized_video_file_name** in both path and url, being the second a custom interpolation and then added the 'normalized_video_file_name' method to video.rb. By doing this we not only achieve a way for paperclip to handle the file by this normalized way, but also have a method to access the normalized file name, plus being able to access the original file name through paperclip video_file_name method. So remember on video_file_name you have the uploaded filename and on normalized_video_file_name you have the server filename.