I'm currently trying to make a photo gallery application where photos are only accessible through a gallery interface. Gallery => has_many :photos, Photo => belongs_to :gallery. All of this is working fine.

However, now I'm trying to give my photos an attached file :image. I did everything Neath says in his tutorial, and I've just added validates_attachment_presence :image. Before the validation, the photo model was working fine except that after saving one with an image, the image never showe开发者_如何学Pythond up. Now, with the validation, after selecting an image to upload, I'm getting a :flash =>

1 error prohibited this photo from being saved

There were problems with the following fields:

    * Image file name must be set.

So what's going on here? Relevant code below:

models/photo

 class Photo < ActiveRecord::Base
    attr_accessible :gallery_id, :name, :rating

    belongs_to :gallery
    validates_associated :gallery

    has_attached_file :image
    validates_attachment_presence :image

  end

views/photos/_form.html.erb

<% form_for [@gallery, @photo], :html => { :multipart => true } do |f| %>
  <%= f.error_messages %>
  <p>
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </p>
  <p>
    <% if @photo.image? %>
      <%= image_tag @photo.image.url %><br />
      <%= link_to @photo.image.url, @photo.image.url %>
    <% end %>
    <%= f.label :image %><br />
    <%= f.file_field :image %>
  </p>
  <p><%= f.submit %></p>
<% end %>

models/gallery.rb

class Gallery < ActiveRecord::Base
  attr_accessible :name, :user_id, :shoot_date

  # destroy all photos when a gallery is destroyed
  has_many :photos, :dependent => :destroy

end

I think I've set up the multipart form correctly, and I think I've had this problem before when I tried a paperclip model without nesting models. Am I missing something?

Update: here is the Mongrel output form the attempted upload transaction:

Processing PhotosController#update (for 127.0.0.1 at 2010-12-05 14:19:29) [PUT]
  Parameters: {"photo"=>{"name"=>"blah", "image"=>#<File:/tmp/RackMultipart20101205-2909-wo2g7z-0>}, "commit"=>"Save changes", "id"=>"10", "gallery_id"=>"3"}
  Gallery Columns (0.6ms)   SHOW FIELDS FROM `galleries`
  Gallery Load (0.1ms)   SELECT * FROM `galleries` WHERE (`galleries`.`id` = 3) 
  Photo Columns (0.7ms)   SHOW FIELDS FROM `photos`
  Photo Load (0.1ms)   SELECT * FROM `photos` WHERE (`photos`.`id` = 10 AND (`photos`.gallery_id = 3)) 
WARNING: Can't mass-assign these protected attributes: image
  SQL (0.1ms)   BEGIN
  CACHE (0.0ms)   SELECT * FROM `galleries` WHERE (`galleries`.`id` = 3) 
  SQL (0.1ms)   ROLLBACK
Rendering template within layouts/application
Rendering photos/edit
Rendered photos/_form (64.1ms)
Completed in 83ms (View: 67, DB: 2) | 200 OK [http://localhost/galleries/3/photos/10]

Figured it out. Threw the mongrel output into google and here we go:

http://railsforum.com/viewtopic.php?id=35544

Basically, they forget to tell you to add :image to the attr_accessible listing.

Photo model changed to 
class Photo < ActiveRecord::Base
    attr_accessible :gallery_id, :name, :rating, :image

    belongs_to :gallery
    validates_associated :gallery

    has_attached_file :image
    validates_attachment_presence :image

  end