acts_as_attachment and belongs_to:

Hi all. I've gotten the acts_as_attachment tutorial to work just fine.
However now i'm trying to do something that's not covered and keep
running into a brick wall. I'm pretty sure this is a simple concept
that I'm just not familiar with yet.

I'd like to association an image with a entry from a different model. I
suppose in other words I'm asking how to update two models from one
controllers create action. Example:

class TrackImage < ActiveRecord::Base
    belongs_to :track
    acts_as_attachment :storage => :file_system, :max_size =>
300.kilobytes, :content_type => :image
    validates_as_attachment
end

class Track < ActiveRecord::Base
  has_many :track_images
end

class Admin::TracksController < ApplicationController
## stuff omitted for brevity's sake
  def create
    @track = Track.new(params[:track])
    if @track.save
      flash[:notice] = 'Track was successfully created.'
      @track_image = TrackImage.create! params[:track_image]
      redirect_to :action => 'list'
    else
      render :action => 'new'
    end
  end
end

## new.rhtml ##

<%= form_tag({:action => 'create'}, :multipart => true) %>
  <%= render :partial => 'form' %>
  <%= submit_tag "Create" %>
<%= end_form_tag %>
<%= link_to 'Back', :action => 'list' %>

## _form.rhtml ##
## stuff omitted for brevity's sake
<p><%= file_field 'track', 'track_image' %></p>

The above code is producting this error:
undefined method `track_image=' for #<Track:0x2278e10>

## _form.rhtml ##
## stuff omitted for brevity's sake
<p><%= file_field 'track', 'track_image' %></p>

The above code is producting this error:
undefined method `track_image=' for #<Track:0x2278e10>

You didn't say specifically but I assume there is where you're getting
the error? Is that correct? If so, it's exactly as it says. There
doesn't exist a track_image method on the Track class. Your
relationship indicates that you have many track_images. Therefore you
have many track_images, not a single track_image method. Try using a
file_field_tag instead or bind the form to the TrackImage class
instead.

Michael