module ExecQueriesWithStandbyTarget
  # Supports queries like User.on_standby.to_a
  def exec_queries
    if standby_target
      Standby.on_standby(standby_target) { super }
    else
      super
    end
  end
end

module ActiveRecord
  class Relation
    attr_accessor :standby_target

    # Supports queries like User.on_standby.count
    alias_method :calculate_without_standby, :calculate

    def calculate(*args)
      if standby_target
        Standby.on_standby(standby_target) { calculate_without_standby(*args) }
      else
        calculate_without_standby(*args)
      end
    end
  end
end

ActiveRecord::Relation.prepend(ExecQueriesWithStandbyTarget)