title: Ruby on Rails thinking-sphinx has many through indexing
body: <p>Cheers! I have <code>tour</code> model with these associations:</p>
  
  <pre><code>  has_many :tour_in_the_countries
    has_many :country, :through =&gt; :tour_in_the_countries
  </code></pre>
  
  <p>And in tour_index.rb</p>
  
  <pre><code>ThinkingSphinx::Index.define :tour, :with =&gt; :active_record do
    indexes :title
    indexes :preview
  end
  </code></pre>
  
  <p>How to add to index country's name in this case?</p>