gistfile1.rb

class Product < ActiveRecord::Base
  define_index do
    indexes :name
  end
end

class Album < Product
end

class SonyAlbum < Album
end

Product.create!(:name => "Product")
Album.create!(:name => "Album")
SonyAlbum.create!(:name => "Sony Album")

# rake thinking_sphinx:rebuild

Product.search.map(&:name) => ["Product", "Album", "Sony Album"]
Album.search.map(&:name) => ["Album", "Sony Album"]
SonyAlbum.search.map(&:name) => ["Sony Album"]

# move define_index into Album

class Product < ActiveRecord::Base
end

class Album < Product
  define_index do
    indexes :name
  end
end

class SonyAlbum < Album
end

# rake thinking_sphinx:rebuild

Product.search.search.map(&:name) => "undefined method `search'" (obvious)
Album.search.search.map(&:name) => ["Album"]
SonyAlbum.search.map(&:name) => []

# Problem: explicit "AND `products`.`type` = 'Album'" in WHERE clause of source album_core_0 in development.sphinx.conf