```ruby
# encoding: utf-8

class AttachmentUploader < CarrierWave::Uploader::Base
  def extension_white_list
    %w(jpg jpeg gif png pdf xlsx docx xls doc txt)
  end
end
```

Add s3 storage dir structure
user
```ruby
# encoding: utf-8

class AttachmentUploader < CarrierWave::Uploader::Base
  def store_dir
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end

  def extension_white_list
    %w(jpg jpeg gif png pdf xlsx docx xls doc txt)
  end
end
```
assistant