gistfile1.rb

# model
class Survey < ActiveRecord::Base
    CONDITIONS = ["surveys.hotel_id IS NOT NULL"]
end

# controller
conditions = Survey::CONDITIONS

unless params[:time_period].blank?
   conditions << "surveys.created_at > '#{params[:time_period].to_i.months.ago}'"
end

logger.info conditions.inspect

# locally, conditions.inspect will always have only one condition fpr the created_at, eg:
# ["surveys.hotel_id IS NOT NULL", "surveys.created_at > '2011-05-21 01:08:19 -0400'"]

# On Amazon EC2, they keep getting added on, eg:
# ["surveys.hotel_id IS NOT NULL", "surveys.created_at > '2011-05-21 01:08:19 -0400'", "surveys.created_at > '2012-05-21 01:08:37 -0400'"]