attachment_fu validation error

I have this class:

   class Logo < ActiveRecord::Base
     has_one :something

     has_attachment :content_type => :image,
                    :storage => :db_file,
                    :max_size => 500.kilobytes
                    :thumbnails => {:web => '150x100', :pdf => '150x100'},
                    :processor => 'MiniMagick'

     validates_as_attachment
   end

OK, logos are working great in the application, resizing, storage, retrieval, ..., fine. But the validation of existing logos fails with (complete trace below)

   Logo.find(:first).valid?
   NameError: undefined local variable or method `full_filename' for #<Logo:0x3561ed8>

And unfortunately that is triggered by something's validates_associated if no logo is uploaded in its edition. I don't see why valid? ends up calling set_size_from_temp_path, sizes were correctly computed and stored on creation:

   pp Logo.find(:first)
   #<Logo:0x35593f0
    @attributes=
     {"content_type"=>"image/jpeg",
      "size"=>"187697",
      "thumbnail"=>nil,
      "id"=>"1",
      "height"=>"768",
      "db_file_id"=>"3",
      "filename"=>"img_1651.jpeg",
      "parent_id"=>nil,
      "width"=>"1024"}>

This happens with all logos in the application, isn't that suspicious? I've not diffed svn with the installed version but both CHANGELOGs start with

   * April 2, 2007 *

-- fxn

   Logo.find(:first).valid?
NameError: undefined local variable or method `full_filename' for #<Logo:0x3561ed8>
         from ./script/../config/../config/../vendor/rails/activerecord/lib/active_record/base.rb:1860:in `method_missing'
         from ./script/../config/../config/../vendor/plugins/attachment_fu/lib/technoweenie/attachment_fu.rb:276:in `temp_paths'
         from ./script/../config/../config/../vendor/plugins/attachment_fu/lib/technoweenie/attachment_fu.rb:270:in `temp_path'
         from ./script/../config/../config/../vendor/plugins/attachment_fu/lib/technoweenie/attachment_fu.rb:236:in `save_attachment?'
         from ./script/../config/../config/../vendor/plugins/attachment_fu/lib/technoweenie/attachment_fu.rb:339:in `set_size_from_temp_path'
         from ./script/../config/../config/../vendor/rails/activerecord/lib/active_record/callbacks.rb:333:in `send'
         from ./script/../config/../config/../vendor/rails/activerecord/lib/active_record/callbacks.rb:333:in `callback'
         from ./script/../config/../config/../vendor/rails/activerecord/lib/active_record/callbacks.rb:330:in `each'
         from ./script/../config/../config/../vendor/rails/activerecord/lib/active_record/callbacks.rb:330:in `callback'
         from ./script/../config/../config/../vendor/rails/activerecord/lib/active_record/callbacks.rb:295:in `valid?'
         from (irb):16

I've seen something: that method is set as a before_validation, that's why it gets called. Following the traces the plugin tries to determine whether the logo needs to be saved in save_attachment? which in the end results in a call to temp_paths

   def temp_paths
     @temp_paths ||= (new_record? || !File.exist?(full_filename)) ? [] : [copy_to_temp_file(full_filename)]
   end

full_filename is implemented by the file system and s3 backends, but it is missing in the database backend which is the one I am using. I don't know enough about the plugin at this moment to propose a suitable fix, but at least I write a custom quick fix and go on with the project.

-- fxn