make attachments polymorphic

app/models/asset.rb

@@ -1,5 +1,6 @@
 class Asset < ActiveRecord::Base
-  has_many :attachments, :include => :page, :dependent => :destroy
+  has_many :attachments, :as => :attachable, :dependent => :destroy
+
   # HACK: incomplete
   AUDIO_FORMATS = [:wav, :mp3, :m4a, :ogg]
   VIDEO_FORMATS = [:mp4, :avi]
@@ -8,6 +9,10 @@ class Asset < ActiveRecord::Base
   validates_presence_of :upload
   delegate :url, :width, :height, :landscape, :portrait, :to => :upload
 
+  def page_attachments
+    attachments.select(&:attached_to_page?)
+  end
+
   def uploads
     []
   end

app/models/attachment.rb

@@ -1,10 +1,10 @@
 require 'acts_as_list'
 
 class Attachment < ActiveRecord::Base
-  belongs_to :asset, :autosave => true
-  belongs_to :page
+  belongs_to :attachable, :polymorphic => true, :autosave => true
+  belongs_to :parent, :polymorphic => true
 
-  acts_as_list :scope => :page_id
+  acts_as_list :scope => :parent_id
 
   def self.reorder(new_order)
     new_order.each_with_index do |id, index|
@@ -13,11 +13,19 @@ def self.reorder(new_order)
     new_order
   end
 
+  def attached_to_page?
+    parent_type == 'Page'
+  end
+
+  def asset
+    attachable if attachable_type == 'Asset'
+  end
+
   def uploads=(new_uploads)
-    (asset || build_asset).uploads=new_uploads
+    (self.attachable ||= Asset.new).uploads=new_uploads
   end
 
   def uploads
-    (asset || build_asset).uploads
+    (self.attachable ||= Asset.new).uploads
   end
 end

app/views/admin/assets/remove.html.erb

@@ -8,16 +8,16 @@
 
 <table class="index" id="assets">
   <tr><td class="name"><%= asset_listing(@asset) %></td></tr>
-  <% if @asset.attachments.any? %>
+  <% if @asset.page_attachments.any? %>
     <tr>
       <th>
         It's being used on the following
-        <%= pluralize(@asset.attachments.size, 'page') %> and will be removed from
+        <%= pluralize(@asset.page_attachments.size, 'page') %> and will be removed from
         there as well:
         </th>
     </tr>
-    <% @asset.attachments.each do |attachment| %>
-      <tr><td><%= attachment.page.title %></td></tr>
+    <% @asset.page_attachments.each do |attachment| %>
+      <tr><td><%= attachment.parent.title %></td></tr>
     <% end %>
   <% end %>
 </table>

assets_extension.rb

@@ -33,7 +33,7 @@ def activate
     ApplicationController.helper(:assets)
     Page.class_eval do
       include AssetTags
-      has_many :attachments, :include => :asset, :order => :position
+      has_many :attachments, :as => :parent, :include => :attachable, :order => :position, :dependent => :destroy
     end
   end
 end

db/migrate/20110321005357_make_attachments_polymorphic.rb

@@ -0,0 +1,17 @@
+class MakeAttachmentsPolymorphic < ActiveRecord::Migration
+  def self.up
+    rename_column :attachments, :page_id, :parent_id
+    add_column :attachments, :parent_type, :string
+    Attachment.update_all 'parent_type = "Page"'
+
+    rename_column :attachments, :asset_id, :attachable_id
+    add_column :attachments, :attachable_type, :string
+    Attachment.update_all 'attachable_type = "Asset"'
+  end
+
+  def self.down
+    warn 'This will delete all Attachments that aren’t attached to pages'
+    remove_column :attachments, :parent_type
+    rename_column :attachments, :parent_id, :page_id
+  end
+end