gistfile1.rb

_form.html.erb
<%= form_for(@gallery) do |f| %>
  <% if @gallery.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@gallery.errors.count, "error") %> prohibited this gallery from being saved:</h2>

      <ul>
      <% @gallery.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </div>

<% f.fields_for :gallery_photos do |gf_form| %>
     <%= gf_form.label :photo, 'Photo:' %>
     <%= gf_form.file_field :photo %>
<% end %>

  <div class="actions">
    <%= f.submit %>
  </div>

<% end %>

class Gallery < ActiveRecord::Base
 has_many :gallery_photos
 accepts_nested_attributes_for :gallery_photos

end

class GalleryPhoto < ActiveRecord::Base
 belongs_to :gallery
  
  has_attached_file :photo, :styles => { :medium => "300x300>", :thumb => "100x100>" }

end