先上代码：

class Micropost < ActiveRecord::Base
  # 省略
  has_many :post_food_relationships, foreign_key: :post_id, dependent: :destroy
  has_many :foods, through: :post_food_relationships

  include ＭicropostCreator
  #省略
end

由于 Micropost 和 Food 是 多对多 的关系，新建一个有食物信息的 Micropost 时就需要写三个表：

1. microposts
2. foods
3. post_food_relationships

这时需要把三者放入一个 transaction 中：

module MicropostCreator extend BasicCreator
  transaction_around :save_with_foods
  logging_before :save_with_foods

  def save_with_foods(foods_parmas)
    # save micropost, foods, post_food_relationships
  end
end  

我希望通过一个方法 transaction_around(*method_names) 来使方法在 transaction 中运行：

module BasicCreator

def transaction_around(*method_names)
    method_names.each do |name|
      m = instance_method(name)

      define_method name do |*params|
        transaction do
          puts "transaction"
          m.bind(self).call(*params)
        end
      end
    end
  end

  def logging_before(*method_names)
    method_names.each do |name|
      m = instance_method(name)

      define_method name do |*params|
        puts "Running #{self.class}##{m.name}(#{params.inspect})"
        m.bind(self).call(*params)
      end
    end
  end
end

发现 transaction_around 必须放在方法声明之后，如何才能无视位置？