ruby-on-rails-3 – 测量单位转换宝石

我需要将kilogramms转换为gramms,升转换成汤匙等.

我想,它应该是这样的：

class Product < ActiveRecord:Base
  acts_as_physical_unit,:volume,:mass,:count
end

class Ingredient < ActiveRecord:Base
  acts_as_physical_unit,:count
end

olive_oil = Product.new(:name => "Olive Oil",:volume => "1000 ml")

caesar_salad = Recipe.new(:name => "Caesar salad",:ingredients => [
    Ingredient.new(:product => [olive_oil],:volume => "5 tablespoons")
  ]

# In ingredients of "Caesar Salad" are 5 tablespoons of "Olive Oil" specified.
# We should create "Caesar Salad" for 50 persons.
# How mutch bottles of "Olive Oil" should be ordered ?
order = OrderItem.new(
  :product => olive_oil,:count => olive_oil.count_for(caesar_salad.ingredients.first)) * 50
)

这样的宝石是否存在？

谢谢.