file upload without activerecord

If I understand correctly what you need then the most simple example would be this:

The controller:

  class UploadController < ApplicationController
  def new

  end

  def create
    name = params[:upload][:file].original_filename
    path = File.join("public", "images", "upload", name)
    File.open(path, "wb") { |f| f.write(params[:upload][:file].read) }
    flash[:notice] = "File uploaded"
    redirect_to "/upload/new"
  end
end

The view:

<% flash.each do |key, msg| %>
    <%= content_tag :div, msg, :class => [key, " message"], :id => "notice_#{key}" %>
<% end %>
<% form_tag '/upload/create', { :multipart => true } do %>
    <p>
    <%= file_field_tag 'upload[file]' %>
    </p>
    <p>
        <%= submit_tag "Upload" %>
    </p>
<% end %>

This would let you upload any file without any checks or validations which in my opinion isn’t that usefull.

If I would do it myself then I would use something like validatable gem or tableless gem just tableless is not supported anymore. These gems would allow you to validate what you’re uploading to make it more sane.