Introduction

This library aids one in handling money and different currencies. Features:

• Provides a Money class which encapsulates all information about an certain amount of money, such as its value and its currency.
• Represents monetary values as integers, in cents. This avoids floating point rounding errors.
• Provides APIs for exchanging money from one currency to another.
• Has the ability to parse a money string into a Money object.

Resources:

• Website: money.rubyforge.org
• RDoc API: money.rubyforge.org
• Git repository: github.com/FooBarWidget/money/tree/master

Download

Install stable releases with the following command:

  gem install money

The development version (hosted on Github) can be installed with:

  gem sources -a http://gems.github.com
  gem install FooBarWidget-money

Usage

Synopsis

  require 'money'

  # 10.00 USD
  money = Money.new(1000, "USD")
  money.cents     # => 1000
  money.currency  # => "USD"

  Money.new(1000, "USD") == Money.new(1000, "USD")   # => true
  Money.new(1000, "USD") == Money.new(100, "USD")    # => false
  Money.new(1000, "USD") == Money.new(1000, "EUR")   # => false

Currency Exchange

Exchanging money is performed through an exchange bank object. The default exchange bank object requires one to manually specify the exchange rate. Here’s an example of how it works:

  Money.add_rate("USD", "CAD", 1.24515)
  Money.add_rate("CAD", "USD", 0.803115)

  Money.us_dollar(100).exchange_to("CAD")  # => Money.new(124, "CAD")
  Money.ca_dollar(100).exchange_to("USD")  # => Money.new(80, "USD")

Comparison and arithmetic operations work as expected:

  Money.new(1000, "USD") <=> Money.new(900, "USD")   # => 1; 9.00 USD is smaller
  Money.new(1000, "EUR") + Money.new(10, "EUR") == Money.new(1010, "EUR")

  Money.add_rate("USD", "EUR", 0.5)
  Money.new(1000, "EUR") + Money.new(1000, "USD") == Money.new(1500, "EUR")

There is nothing stopping you from creating bank objects which scrapes www.xe.com for the current rates or just returns rand(2):

  Money.default_bank = ExchangeBankWhichScrapesXeDotCom.new

Ruby on Rails

Use the compose_of helper to let Active Record deal with embedding the money object in your models. The following example requires a cents and a currency field.

  class ProductUnit < ActiveRecord::Base
    belongs_to :product
    composed_of :price, :class_name => "Money", :mapping => [%w(cents cents), %w(currency currency)]

    private
      validate :cents_not_zero

      def cents_not_zero
        errors.add("cents", "cannot be zero or less") unless cents > 0
      end

      validates_presence_of :sku, :currency
      validates_uniqueness_of :sku
  end

Default Currency

By default Money defaults to USD as its currency. This can be overwritten using

  Money.default_currency = "CAD"

If you use Rails, then environment.rb is a very good place to put this.