How to display images in the list action of rails_admin?
===

I have a self-associating model which allows the user to define a "parent photo", in order to group them together.

My model:

    class Photo < ActiveRecord::Base

      attr_accessible :image, :parent_photo

      has_attached_file :image, :styles => { :medium => "300x300>", :thumb => "100x100>" }

      validates_attachment :image, 
        :presence => true,
        :size => { :in => 20..2000.kilobytes },
        :content_type => { :content_type => [ 'image/jpeg', 'image/png' ] }

      belongs_to :parent, class_name: "Photo", foreign_key: :parent_photo

      def associated_photos
        Photo.find_by_parent_photo(id)
      end

    end

And in my rails_admin initializer:

    ..

      config.model Photo do

        list do
          field :image
          field :associated_photos     
        end
      end
    end

How do I retrieve the actual thumbnail for use in the list action?