gistfile1.rb

## With this code instead of passing a file and being a file object in the params like:
##   Parameters: {"commit"=>"Save changes", "authenticity_token"=>"CNHWuiMsSkwK4x3biFGogUnRU2kutvKuCfOTH2Y+PO4=", "painting"=>{"image"=>#<File:/tmp/RackMultipart20100102-3131-9c0z0-0>}}

## it passes just a name of the file like so:

##   Parameters: {"action"=>"create", "authenticity_token"=>"atvaDTdf2yhQKea8t/VBhYyT2ENyK9B/ZYGQSRq9414=", "painting"=>{"title"=>"g", "height"=>"1", "picture"=>"Tweetie.gif", "width"=>"1"}, "controller"=>"admin/paintings"}


## Model

class Painting < ActiveRecord::Base

  has_attached_file :picture

  validates_presence_of :title, :height, :width
  validates_attachment_presence :picture

end

## Controller

class Admin::PaintingsController < AdminController

  def new
    @painting = Painting.new
  end

  def create
    @painting = Painting.new(params[:painting])
    if @painting.save
      redirect_to admin_paintings_path
    else
      render :new
    end
  end

end

## View

- content_for :heading do
  %h2.head= "Add Painting"

- form_for [:admin, @painting], :html => { :mulitpart => true } do |f|
  = f.error_messages
  %fieldset
    .input_field
      = f.label :title
      = f.text_field :title, :class => "input mediumfield"
    .input_field
      = f.label :height
      = f.text_field :height, :class => "input smallfield"
      %span (mm)
    .input_field
      = f.label :width
      = f.text_field :width, :class => "input smallfield"
      %span (mm)
    .input_field
      = f.label :picture
      = f.file_field :picture

    %input{ :value => "Submit", :class => "submit", :type => "submit"}

%div{ :class => "clear"}