如何在django模板中获取引用属性

我在谷歌应用程序引擎上使用aep

class Link():
     bag  = db.Referencepropery(Bag) #bag have name, id and other property
     name = db.Stringpropery


object_query = Link.all();
p = paginator( object_query)
object_list = p.page(1);
prefetch_references( object_list.object_list, 'bag')

render_to_response(...,{'object_list':object_list.object_list},...)


#template
{% for object in object_list%}
 {{object.bag.id}} <!--failed to get any value, why???/-->
{% end %}