title: Rails polymorphic assosication - on validation error render parent show action with flash message
body: <p>I have articles, profiles, and comments. There is a polymorphic association between articles/profiles and comments called commentable.</p>
  
  <p>On success creating a new comment I return to the commentable parent object with a sucess flash and I would like to do the same with the appropriate error flash on validation errors.</p>
  
  <p>What should I pass to render?</p>
  
  <pre><code>def create
    @commentable = find_commentable
    @comment = @commentable.comments.build(params[:comment])
    if @comment.save
      flash[:notice] = "Successfully created comment."
      redirect_to @commentable
    else
      render '??path_to_commentable_object_show??'
    end
  end
  </code></pre>
  
  <p>I guess I could build the path by grabbing the commentable class name and lowercasing it... but that seems awkward.</p>