title: STI & Polymorphic association & user_id
body: <p>So I have an assets model which is inherited by images and files as STI. Products has many images as assetable. This polymorphic association is working fine but I can't figure out how to add the user_id to every asset. A asset always belongs to a user no matter if its an image or file. Please look at my code below. I'm pretty sure there's something I need to do within the controllers create method but I'm not sure what? I've tried merging :user_id but this just returns nil when looking at the console log. Ideally what I'd also like to do is @user.images which will display all the images that the user has uploaded or even @user.files</p>
  
  <pre><code>class User &lt; ActiveRecord::Base
    has_many :products
    has_many :assets
  end
  
  class Asset &lt; ActiveRecord::Base
    belongs_to :assetable, :polymorphic =&gt; true
    belongs_to :user
  end
  
  class Image &lt; Asset
    mount_uploader :filename, ImageUploader
    attr_accessible :filename, :assets
  end
  
  class Product &lt; ActiveRecord::Base
    belongs_to :user
  
    has_many :images, as: :assetable
    accepts_nested_attributes_for :images 
  
    attr_accessible :name, :price, :images_attributes
    validates_presence_of :name
  end
  
  class ProductsController &lt; ApplicationController
   def create
     @product = Product.new(params[:product])
     @product.user_id = current_user.id
  
     params[:product][:images_attributes].each do |key, image|
       # image.user_id = current_user.id
       image.merge(:user_id =&gt; 1)
     end
  
     @product.save
   end
  end
  </code></pre>