This library aids one in handling money and different currencies.
- Provides a
Money
class which encapsulates all information about an certain amount of money, such as its value and its currency. - Provides a
Money::Currency
class which encapsulates all information about a monetary unit. - Represents monetary values as integers, in cents. This avoids floating point rounding errors.
- Represents currency as
Money::Currency
instances providing an high level of flexibility. - Provides APIs for exchanging money from one currency to another.
- Has the ability to parse a money and currency strings into the corresponding Money/Currency object.
Install stable releases with the following command:
gem install money
The development version (hosted on Github) can be installed with:
git clone git://github.com/RubyMoney/money.git
cd money
rake install
require 'money'
# 10.00 USD
money = Money.new(1000, "USD")
money.cents #=> 1000
money.currency #=> Currency.new("USD")
# Comparisons
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
Money.new(1000, "USD") != Money.new(1000, "EUR") #=> true
# Arithmetic
Money.new(1000, "USD") + Money.new(500, "USD") == Money.new(1500, "USD")
Money.new(1000, "USD") - Money.new(200, "USD") == Money.new(800, "USD")
Money.new(1000, "USD") / 5 == Money.new(200, "USD")
Money.new(1000, "USD") * 5 == Money.new(5000, "USD")
# Currency conversions
some_code_to_setup_exchange_rates
Money.new(1000, "USD").exchange_to("EUR") == Money.new(some_value, "EUR")
Currencies are consistently represented as instances of Money::Currency
.
The most part of Money
APIs allows you to supply either a String
or a
Money::Currency
.
Money.new(1000, "USD") == Money.new(1000, Currency.new("USD"))
Money.new(1000, "EUR").currency == Currency.new("EUR")
A Money::Currency
instance holds all the information about the currency,
including the currency symbol, name and much more.
currency = Money.new(1000, "USD").currency
currency.iso_code #=> "USD"
currency.name #=> "United States Dollar"
To define a new Money::Currency
simply add a new item to the
Money::Currency::TABLE
hash, where the key is the identifier for the currency
object and the value is a hash containing all the currency attributes.
Money::Currency::TABLE[:usd] = {
:priority => 1,
:iso_code => "USD",
:iso_numeric => "840",
:name => "United States Dollar",
:symbol => "$",
:subunit => "Cent"
:subunit_to_unit => 100,
:separator => ".",
:delimiter => ","
}
The pre-defined set of attributes includes:
:priority
a numerical value you can use to sort/group the currency list:iso_code
the international 3-letter code as defined by the ISO 4217 standard:iso_numeric
the international 3-digit code as defined by the ISO 4217 standard:name
the currency name:symbol
the currency symbol (UTF-8 encoded):subunit
the name of the fractional monetary unit:subunit_to_unit
the proportion between the unit and the subunit:separator
character between the whole and fraction amounts:delimiter
character between each thousands place
All attributes are optional. Some attributes, such as :symbol
, are used by
the Money class to print out a representation of the object. Other attributes,
such as :name
or :priority
, exist to provide a basic API you can take
advantage of to build your application.
The priority attribute is an arbitrary numerical value you can assign to the
Money::Currency
and use in sorting/grouping operation.
For instance, let's assume your Rails application needs to render a currency selector like the one available here. You can create a couple of custom methods to return the list of major currencies and all currencies as follows:
# Returns an array of currency id where
# priority < 10
def major_currencies(hash)
hash.inject([]) do |array, (id, attributes)|
priority = attributes[:priority]
if priority && priority < 10
array[priority] ||= []
array[priority] << id
end
array
end.compact.flatten
end
# Returns an array of all currency id
def all_currencies(hash)
hash.keys
end
major_currencies(Money::Currency::TABLE)
# => [ :usd, :eur, :bgp, :cad ]
all_currencies(Money::Currency::TABLE)
# => [ :aed, :afn, all, ... ]
By default Money
defaults to USD as its currency. This can be overwritten
using:
Money.default_currency = Money::Currency.new("CAD")
If you use Rails, then environment.rb
is a very good place to put this.
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
XE for the current rates or just returns rand(2)
:
Money.default_bank = ExchangeBankWhichScrapesXeDotCom.new
The following is a list of Money.gem compatible currency exchange rate implementations.
Use the composed_of
helper to let Active Record deal with embedding the money
object in your models. The following example requires 2 columns:
:price_cents, :integer, :default => 0, :null => false
:currency, :string
Then in your model file:
composed_of :price,
:class_name => "Money",
:mapping => [%w(price_cents cents), %w(currency currency_as_string)],
:constructor => Proc.new { |cents, currency| Money.new(cents || 0, currency || Money.default_currency) },
:converter => Proc.new { |value| value.respond_to?(:to_money) ? value.to_money : raise(ArgumentError, "Can't convert #{value.class} to Money") }
For Money 2.2.x and previous versions, simply use the following composed_of
definition:
composed_of :price,
:class_name => "Money",
:mapping => [%w(cents cents), %w(currency currency)],
:constructor => Proc.new { |cents, currency| Money.new(cents || 0, currency || Money.default_currency) }
Note the difference in the currency column mapping (currency_as_string vs. currency) - this matters! For further details read the full discussion here.