Rails Searchkick / Elasticsearch has_many and belongs_to associations

Im trying to use Searchkick to run a search and return based on multiple models.

My book model contains this

class Book < ActiveRecord::Base

  searchkick

  has_many :book_subjects
  has_many :subjects, through: :book_subjects

  belongs_to :author
  belongs_to :publisher

end

and then my controller has this

def index

 if params[:search].present?
   @books = Book.search(params[:search], operator: "or")
 else
  @books = Book.all
 end
end

I want the search results to search the associated models and return any results there too -- so the boo subject name, the author and the publisher.

thanks