Rails3とRails4の違いの1つに has_many のオプションがある。

# Rails3
class Course < ActiveRecord::Base
  has_many :students, order: :name, include: [:parents, :brothers], dependent: :destroy
end

# Rails4
class Course < ActiveRecord::Base
  has_many :students, ->{ order(:name).includes(:parents, :brothers) }, dependent: :destroy
end

Rails4では orderinclude が使えなくなってる。

しかし、1つのソースでRails3とRails4に対応したい場合どうしようか?

module AssocOpts
  extend ActiveSupport::Concern

  module ClassMethods
    def assoc_opts(options)
      return [options] if Gem::Version.new(Rails.version) < Gem::Version.new('4.0.0')

      order_option = options.delete(:order)
      include_option = options.delete(:include)
      if order_option && include_option
        [Proc.new { order(order_option).includes(include_option) }, options]
      elsif order_option
        [Proc.new { order(order_option) }, options]
      elsif include_option
        [Proc.new { includes(include_option) }, options]
      else
        [options]
      end
    end
  end
end

# Rails3 and Rails4
class Course < ActiveRecord::Base
  include AssocOpts

  has_many :students, *assoc_opts(order: :name, include: [:parents, :brothers], dependent: :destroy)
end

とまあこんな感じでどうかな?