Optimizer Hints

application_record.rb

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true

  def self.optimizer_hints(hints)
    hints.present? ? extending(OptimizerHints.new(hints.to_s)) : all
  end

  class OptimizerHints < Module
    def initialize(hints)
      define_method(:build_arel) do |*args|
        super(*args).tap do |arel|
          ctx = arel.instance_variable_get(:@ctx)
          if ctx.set_quantifier
            ctx.set_quantifier = Arel.sql("/*+ #{hints} */ DISTINCT")
          else
            ctx.set_quantifier = Arel.sql("/*+ #{hints} */")
          end
        end
      end
    end
  end
  private_constant :OptimizerHints
end