CarrierWave

file_uploader.rb

# encoding: utf-8

class FileUploader < CarrierWave::Uploader::Base
  include CarrierWave::RMagick
  storage :file

  def store_dir
    "photos/#{model.attachable_id}"
  end

  process :resize_to_limit => [500, 500]
  process :convert => 'png'

  version :medium do
    process :resize_to_limit => [250, 250]
    process :convert => 'png'
    def full_filename (for_file = model.file)
      "thumb_#{model.id}_medium.png"
    end
  end

  version :small do
    process :resize_to_limit => [50, 50]
    process :convert => 'png'
    def full_filename (for_file = model.file)
      "thumb_#{model.id}_small.png"
    end
  end

  def filename
    "#{model.id}_original.png" if original_filename
  end
end

show.html.haml

#title
  %h1
    = @ad.title
#ad_content
  %b Treść ogłoszenia:
  = @ad.ad_content
%br
- if @ad.photos.present?
  - @ad.photos.each do |p|
    #photos
      = image_tag("../../photos/#{@ad.id}/thumb_#{p.id}_small.png")