Elasticsearch, Tire, and Nested queries / associations with ActiveRecord

I'm using ElasticSearch with Tire to index and search some ActiveRecord models, and I've been searching for the "right" way to index and search associations. I haven't found what seems like a best practice for this, so I wanted to ask if anyone has an approach that they think works really well.

As an example setup (this is made up but illustrates the problem), let's say we have a book, with chapters. Each book has a title and author, and a bunch of chapters. Each chapter has text. We want to index the book's fields and the chapters' text so you can search for a book by author, or for any book with certain words in it.

class Book < ActiveRecord::Base
  include Tire::Model::Search
  include Tire::Model::Callbacks

  has_many :chapters

  mapping do
    indexes :title, :analyzer => 'snowball', :boost => 100
    indexes :author, :analyzer => 'snowball'
    indexes :chapters, type: 'object', properties: {
      chapter_text: { type: 'string', analyzer: 'snowball' }
    }
  end
end

class Chapter < ActiveRecord::Base
  belongs_to :book
end

So then I do the search with:

s = Book.search do
  query { string query_string }
end

That doesn't work, even though it seems like that indexing should do it. If instead I index:

indexes :chapters, :as => 'chapters.map{|c| c.chapter_text}.join('|'), :analyzer => 'snowball'

That makes the text searchable, but obviously it's not a nice hack and it loses the actual associated object. I've tried variations of the searching, like:

s = Book.search do
  query do
    boolean do
      should { string query_string }
      should { string "chapters.chapter_text:#{query_string}" }
    end
  end
end

With no luck there, either. If anyone has a good, clear example of indexing and searching associated ActiveRecord objects using Tire, it seems like that would be a really good addition to the knowledge base here.

Thanks for any ideas and contributions.