the query selects all ids from the full branch from the nested set

product.rb

class Product
  define_index do
    # ...
    has %(
      (
        SELECT GROUP_CONCAT(IFNULL(parent.`id`, '0') SEPARATOR ',')
        FROM `categories` AS node,
        `categories` AS parent
        WHERE node.`merchant_id` = `products`.`merchant_id` AND
          parent.`merchant_id` = `products`.`merchant_id` AND
          node.`lft` BETWEEN parent.`lft` AND parent.`rgt` AND node.`id` = `category_id`
        ORDER BY parent.`lft`
      )
    ), :source => :query, :type => :multi, :as => :category_ids, :facet => true
  end
end

The query selects all ids from the full branch from the nested set of categories per merchant (see http://dev.mysql.com/tech-resources/articles/hierarchical-data.html "Retrieving a Single Path"). I want to have a facet for that but here's what Thinking Sphinx is giving me (cut the gem directory for brevity):

Product.facets('adidas')
NoMethodError: undefined method ( SELECT GROUP_CONCAT(IFNULL(parent.id, '0') SEPARATOR ',') FROMcategoriesAS node, categoriesAS parent WHERE node.merchant_id=products.merchant_idAND parent.merchant_id=products.merchant_idAND node.lftBETWEEN parent.lftAND parent.rgtAND node.id=category_id ORDER BY parent.lft ) ' for #<Product:0x104cc1410> from GEM_DIR/activerecord-2.3.8/lib/active_record/attribute_methods.rb:264:inmethod_missing'
from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/facet.rb:107:in send' from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/facet.rb:107:intranslate'
from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/facet.rb:80:in value' from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/facet_search.rb:125:inadd_from_results'
from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/search.rb:264:in each_with_match' from (irb):33:ineach_with_index'
from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/search.rb:263:in each' from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/search.rb:263:ineach_with_index'
from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/search.rb:263:in each_with_match' from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/facet_search.rb:124:inadd_from_results'
from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/facet_search.rb:50:in populate' from (irb):33:ineach_with_index'
from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/facet_search.rb:47:in each' from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/facet_search.rb:47:ineach_with_index'
from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/facet_search.rb:47:in populate' from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/facet_search.rb:13:ininitialize'
from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/search_methods.rb:422:in new' from GEM_DIR/thinking-sphinx-1.4.0/lib/thinking_sphinx/search_methods.rb:422:infacets'
from (irb):33
from :0>>

It's Rails 2.3, Thinking Sphinx 1.4.0, Riddle 1.2.1 and Sphinx 0.9.9 r2117.