app/uploaders/coderwall_uploader.rb
class CoderwallUploader < CarrierWave::Uploader::Base
include CarrierWave::MiniMagick
include ::CarrierWave::Backgrounder::Delay
def extension_white_list
%w(jpg jpeg gif png)
end
def store_dir
"uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
end
end