ARel named function helpers

arel_math_named_functions.rb

# Collection of helpers for math-related ARel NamedFunctions.
#
# Include this in classes that need to do trig with DB functions. Lets you write
# cleaner code, like:
#
#   dist = acos(sin(lat) * sin(arel_lat_field) +
#               cos(lat) * cos(arel_lat_field) * cos(arel_lng_field)) * EARTH_RADIUS_KM
#   band_num = round(dist / ring_width, 0)
#   band_num.to_sql
#   # => round(abs(acos(
#          (sin(0.6639333703683045) *
#           sin("places"."latitude" * 0.017453292519943295) +
#           cos(0.6639333703683045) *
#           cos("places"."latitude" * 0.017453292519943295) *
#           cos("places"."longitude" * 0.017453292519943295))
#        ) * 6371) / 10, 0)
#
module Arel
  module Math

    module Extras
      FUNCTIONS = %w(cos sin acos round)

      FUNCTIONS.each do |func|
        define_method(func) do |*args|
          Arel::Nodes::NamedFunction.new(func, args).extend(Arel::Math)
        end
      end
    end

  end
end