reverse-benchmark.rb

require 'benchmark'

module Arel
  module Nodes
    class Ordering
    end
  end
end

def old_reverse_sql_order(order_query)
  order_query = ["#{quoted_table_name}.#{quoted_primary_key} ASC"] if order_query.empty?

  order_query.map do |o|
    case o
    when Arel::Nodes::Ordering
      o.reverse
    when String, Symbol
      o.to_s.split(',').collect do |s|
        s.strip!
        s.gsub!(/\sasc\Z/i, ' DESC') || s.gsub!(/\sdesc\Z/i, ' ASC') || s.concat(' DESC')
      end
    else
      o
    end
  end.flatten
end

def new_reverse_sql_order(order_query)
  order_query = ["#{quoted_table_name}.#{quoted_primary_key} ASC"] if order_query.empty?

  order_query.map do |o|
    case o
    when Arel::Nodes::Ordering
      o.reverse
    when String, Symbol
      s = o.to_s.gsub(/\s((desc)|(asc))\s*(,|\Z)/i) { |m| " #{$2 ? 'ASC' : 'DESC'}#{$4}" }
      s.match(/\s(de|a)sc\Z/i) ? s : s.concat(" DESC")
    else
      o
    end
  end.flatten
end

query = ['SELECT  "tests".* FROM "tests" ORDER BY COALESCE(updated_at, created_at) ASC LIMIT 1']
n = 10_000

Benchmark.bmbm do |x|
  x.report('old') { n.times { old_reverse_sql_order(query) } }
  x.report('new') { n.times { new_reverse_sql_order(query) } }
end