Question

My models:

class NewsItem < ActiveRecord::Base
  has_many :file_uploads, :as => :uploadable
  accepts_nested_attributes_for :file_uploads, :allow_destroy => true
end


class FileUpload < ActiveRecord::Base
  belongs_to :uploadable, :polymorphic => true
  has_attached_file :upload, :styles => {:thumb => '100x100>'}
end

Form Code (nested within NewsItem)

...

<%= f.fields_for :file_uploads do |upload| %>
  <div class="file_upload">
    <%= upload.file_field :upload %>
  </div>

  ...

<% end %>

...

On submit I get the following error: “unknown attribute: upload”. Here are the params:

{"utf8"=>"✓",
 "authenticity_token"=>"MBfxJ4XTizCXv3Mpu971VHCm60bS3Y84Kdxfe+VJD2w=",
 "news_item"=>{"title"=>"",
 "body"=>"",
 "published_date"=>"",
 "file_uploads_attributes"=>{"0"=>{"upload"=>#<ActionDispatch::Http::UploadedFile:0x000001070112a8 @original_filename="rails-dd352fc2630e5f9aa5685ef1d7fe5997.png",
 @content_type="image/png",
 @headers="Content-Disposition: form-data; name=\"news_item[file_uploads_attributes][0][upload]\"; filename=\"rails-dd352fc2630e5f9aa5685ef1d7fe5997.png\"\r\nContent-Type: image/png\r\n",
 @tempfile=#<File:/var/folders/hb/2bkct63171lck8d3sg0xfq0c0000gn/T/RackMultipart20111204-3216-71in7a>>,
 "name"=>"",
 "caption"=>""}}},
 "commit"=>"Create News item"}

I’m using Rails 3.1.3 and paperclip “~> 2.4”.

Answer 1

Restarting the rails app fixed the problem. I’m guessing I installed the gem but did not restart, leading to the error above. Lesson learned: always restart after installing a gem.