Railsでupload

mac$ rails new upload
mac$ cd upload/
mac$ bundle install
mac$ mkdir public/data
mac$ rails g model data_file name:string directory:string path:string
mac$ rails g controller upload
mac$ rake db:migrate

app/config/routes.rb

Upload::Application.routes.draw do
  get "upload" => "upload#index"
  post "uploadfile" => "upload#uploadfile"
end

app/controllers/upload_controller.rb

class UploadController < ApplicationController
  def index
     render :file => '/upload/uploadfile.rhtml'
  end
  
  def uploadfile
    post = DataFile.save(params[:file])  
    render :text => "File has been uploaded successfully"
  end
end

app/models/data_file.rb

class DataFile < ActiveRecord::Base
  def self.save(upload)
    name =  upload.original_filename
    directory = "public/data"
    # create the file path
    path = File.join(directory, name)
    # write the file
    File.open(path, "wb") { |f| f.write(upload.read) }
  end
end

app/views/upload/uploadfile.rhtml

<%= form_tag '/uploadfile', :multipart => true do %>
  <label for="file">File to Upload</label> <%= file_field_tag "file" %>
  <%= submit_tag %>
<% end %>

http://api.rubyonrails.org/classes/ActionView/Helpers/FormTagHelper.html