title: ActiveAdmin forms with has_many - belongs_to relationships?
body: <p>I have the models Home and Photo, which have a has_many - belongs_to relationship (a polymorphic relationship, but I dont think that matters in this case). I am now setting up  active admin and I would like admins to be able to add photos to homes from the homes form.</p>
  
  <p>The photos are managed by the CarrierWave gem, which I dont know if will make the problem easier or harder.</p>
  
  <p>How can I include form fields for a different model in the Active Admin Home form? Any experience doing something like this? </p>
  
  <pre><code>class Home &lt; ActiveRecord::Base
    validates :name, :presence =&gt; true,
                       :length =&gt; { :maximum =&gt; 100 }
    validates :description, :presence =&gt; true      
    has_many :photos, :as =&gt; :photographable
  
  end
  
  
  class Photo &lt; ActiveRecord::Base
      belongs_to :photographable, :polymorphic =&gt; true
      mount_uploader :image, ImageUploader
  end
  </code></pre>