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 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