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.