render :json does not accept options

I'd love to use render :json but it seems its not as flexible. Whats the right way to do this?

respond_to do |format|
  format.html # index.html.erb
  format.xml  { render :xml => @things }

  #This is great
  format.json { render :text => @things.to_json(:include => :photos) }

  #This doesn't include photos
  format.json { render :json => @things, :include => :photos }
end

From stackoverflow

• I've done something similar with render :json. This is what worked for me:

  respond_to do |format|
      format.html # index.html.erb
      format.json  { render :json => @things.to_json(:include => { :photos => { :only => [:id, :url] } }) }
  end
  

  swilliams : Thanks, this helped me out too.