How do you include json attributes when using "respond_with"?

I have a controller action that returns JSON data.

  def create
    @comment = @site_update.comments.new
    @comment.attributes = params[:comment]
    @comment.author = current_user

    if @comment.save
      respond_with @comment, :include => :author
    else
      respond_with @comment.errors
    end
  end

This is obviously not working. How can I include the :author of the
comment with the respond_with method?

Thanks

Actually, it is working.... my bad... the problem is something else.

For some reason, it's trying to find 'comment_url', but this does not
exist because comment is a nested resource of another model.

I'll have to look at how to stop it from trying to find a url - it's
just not required here.

To those having the same with problem with nested resources, this is
the solution:

  def create
    @comment = @site_update.comments.new
    @comment.attributes = params[:comment]
    @comment.author = current_user

    if @comment.save
      respond_with @site_update, @comment, :include => :author
    else
      respond_with @site_update, @comment.errors
    end
  end