Uploading files - undefined method 'attr_accessible'

I checked out a Rails sample project, for jquery fileuploads The project itself works, but it's running on 3.2.13.

Now I want to use this code in my own Project, which is based on Rails 4.2.3.

First it didn't work, cause I ran into the error undefined method 'attr_accessible' for #<Class:0x007f7428f82f98>

I found out, that there was a change in Rails 4.1, regarding the "mass alignment". Now I am trying to convert this to Rails 4...

Here is my Upload model:

class Upload < ActiveRecord::Base
  attr_accessible :upload
  has_attached_file :upload

  include Rails.application.routes.url_helpers

  def to_jq_upload
    {
      "name" => read_attribute(:upload_file_name),
      "size" => read_attribute(:upload_file_size),
      "url" => upload.url(:original),
      "delete_url" => upload_path(self),
      "delete_type" => "DELETE"
    }
  end

end

I have deleted everything inside the model-class, and got rid of the error. But now my Rails Application does not accept the uploads. (Nothing happens, when I try to upload a file) I have added the following code to my controller, but it still doesn't accept my uploaded files.

uploads_controller:

def upload_params
  params.require(:upload).permit(:name, :size, :url, :delete_url, :delete_type)
end

Can you guys help me, to get this to work on Rails 4?

Best regards