How to index aggregate association fields with thinking sphinx

Question

So, I'm trying to figure out how to have aggregate fields in my sphinx index. (Count, and AVG)

I have a model named business_profile, which has a has_many association to business_feedbacks:

class BusinessProfile < ActiveRecord::Base
    has_many :business_feedbacks
    #...
end

Trying to add aggregate fields for count, and avg:

ThinkingSphinx::Index.define(:business_profile, with: :active_record, delta: ThinkingSphinx::Deltas::DatetimeDelta) do
    # indexes ... fields
    has 'COUNT(business_feedbacks.id)', as: :feedback_count
    has 'AVG(business_feedbacks.recommend)', as: :feedback_recommend
end 

I get this error when I try to rebuild my index (rake ts:rebuild):

ThinkingSphinx::MissingColumnError: column COUNT(business_feedbacks.id) does not exist

What can I do to add these aggregate fields to my index? I would like to be able to sort results by feedback_count, or feedback_recommend.

Answer 1

Because you're not referring to columns directly, you'll need to specify the type manually:

has 'COUNT(business_feedbacks.id)',      as: :feedback_count,     type: :integer
has 'AVG(business_feedbacks.recommend)', as: :feedback_recommend, type: :integer

… or if the recommend column is something other than an integer, you can change the average type accordingly.