Ruby on Rails

I am using elasticsearch for querying in my application. Lets say there
are 2 models

Class Topic
   has_many :posts
and

Class Article
  has_many :comments

I want to do a combined search on both these models and my query looks
like:

Tire.search [Article, Topic], {:load => {:include => [:posts,
:comments]}} do |search|
...
end
This is where I encounter a problem. I get the

Association named comments not found

error. I think this is because Topic model doesn't have the association
comments and I think the same thing will happen for posts with the
Article model.

Is there anyway to solve this problem? I was thinking maybe something
like

:include => ['topic.posts', 'article.comments']