Polymorphic index? No problems!

If you use thinking-sphinx, this is a nice trick if you need to index polymorphic attributes.

In our case, we have questions that could belong to campaigns or startups. So those questions are polymorphic. But we still need to index them. Here is the description of the index in pure SQL:

indexes "CASE questions.subject_type 
  WHEN 'Campaign' THEN (
    SELECT campaigns.name
    FROM campaigns
    WHERE campaigns.id = questions.subject_id
  )
  WHEN 'Startup' THEN (
    SELECT startups.name
    FROM startups
    WHERE startups.id = questions.subject_id
  )
  END", :as => :startup

Thanks @pedrocarrico!