file_send confused

Anyone see where I am going wrong here?

Error = undefined method `filename='

Model

class Upload < ActiveRecord::Base
      def upload=(upload_field)
        self.filename = upload_field.original_filename
        self.content_type = upload_field.content_type.chomp
        self.binary_data = upload_field.read
      end

end

Controller

def upload
    @upload = Upload.find(params[:id])
    send_file(@upload.file,
      :filename => @upload.name,
      :type => @upload.content_type,
      :disposition => "inline")
  end

Form

<div id="UploadFileBox">
<b>Upload a file:<br/></b>
<% form_tag({:action => 'create'}, :multipart => true) do %>
<%= file_field("upload", "upload") %><%= submit_tag("Upload file") %>
<% end %>

Thanks for any help.
Lynn