Money

acts_as_money is a fairly trivial plugin that makes it easier to work with the money gem. It's available in Rubygems - just 'gem install acts_as_money'.

class Product < ActiveRecord::Base
  acts_as_money
  money :price
end

This assumes that there are 2 columns in the database, cents (integer) and currency (string). These fields can be changed by setting the :cents and :currency options. To use the default currency, you can simple set :currency to false

class Room < ActiveRecord::Base
  acts_as_money
  money :rate, :cents => :rate_in_cents, :currency => :rate_currency
  money :discount, :cents => :discount_in_cents, :currency => false
end

By default, your money field will default to a value of 0. If you require it to default to nil, you may set the :allow_nil option:

class Meal < ActiveRecord::Base
  acts_as_money  
  money :bill, :allow_nil => true
end

m = Meal.new
m.bill #returns nil

r = Room.new
r.rate      #returns <Money:0x24fd53a6 @currency="USD", @cents=0>

acts_as_money allows you to pass a String, Fixnum, Float or Money object as a parameter to the setter, and it will call #to_money to convert it to a Money object. This makes it convenient for using money fields in forms.

r = Room.new :rate => "100.00"
r.rate                            # returns <Money:0x249ef9c @currency="USD", @cents=10000>