RubyMoney - Money

⚠️ Please read the migration notes before upgrading to a new major version.

If you miss String parsing, check out the new monetize gem.

Contributing

See the Contribution Guidelines

Introduction

A Ruby Library for dealing with money and currency conversion.

Features

Provides a Money class which encapsulates all information about a 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 a high level of flexibility.
Provides APIs for exchanging money from one currency to another.

Resources

Notes

Your app must use UTF-8 to function with this library. There are a number of non-ASCII currency attributes.

Downloading

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

Usage

require 'money'

# explicitly define locales
I18n.config.available_locales = :en
Money.locale_backend = :i18n

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

# Comparisons
Money.from_cents(1000, "USD") == Money.from_cents(1000, "USD")   #=> true
Money.from_cents(1000, "USD") == Money.from_cents(100, "USD")    #=> false
Money.from_cents(1000, "USD") == Money.from_cents(1000, "EUR")   #=> false
Money.from_cents(1000, "USD") != Money.from_cents(1000, "EUR")   #=> true

# Arithmetic
Money.from_cents(1000, "USD") + Money.from_cents(500, "USD") == Money.from_cents(1500, "USD")
Money.from_cents(1000, "USD") - Money.from_cents(200, "USD") == Money.from_cents(800, "USD")
Money.from_cents(1000, "USD") / 5                            == Money.from_cents(200, "USD")
Money.from_cents(1000, "USD") * 5                            == Money.from_cents(5000, "USD")

# Unit to subunit conversions
Money.from_amount(5, "USD") == Money.from_cents(500, "USD")  # 5 USD
Money.from_amount(5, "JPY") == Money.from_cents(5, "JPY")    # 5 JPY
Money.from_amount(5, "TND") == Money.from_cents(5000, "TND") # 5 TND

# Currency conversions
some_code_to_setup_exchange_rates
Money.from_cents(1000, "USD").exchange_to("EUR") == Money.from_cents(some_value, "EUR")

# Swap currency
Money.from_cents(1000, "USD").with_currency("EUR") == Money.from_cents(1000, "EUR")

# Formatting (see Formatting section for more options)
Money.from_cents(100, "USD").format #=> "$1.00"
Money.from_cents(100, "GBP").format #=> "£1.00"
Money.from_cents(100, "EUR").format #=> "€1.00"

Currency

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.from_cents(1000, "USD") == Money.from_cents(1000, Money::Currency.new("USD"))
Money.from_cents(1000, "EUR").currency == Money::Currency.new("EUR")

A Money::Currency instance holds all the information about the currency, including the currency symbol, name and much more.

currency = Money.from_cents(1000, "USD").currency
currency.iso_code #=> "USD"
currency.name     #=> "United States Dollar"

To define a new Money::Currency use Money::Currency.register as shown below.

curr = {
  priority:            1,
  iso_code:            "USD",
  iso_numeric:         "840",
  name:                "United States Dollar",
  symbol:              "$",
  subunit:             "Cent",
  subunit_to_unit:     100,
  decimal_mark:        ".",
  thousands_separator: ","
}

Money::Currency.register(curr)

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
:decimal_mark character between the whole and fraction amounts
:thousands_separator character between each thousands place

All attributes except :iso_code 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.

:priority

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, :gbp, :aud, :cad, :jpy]

all_currencies(Money::Currency.table)
# => [:aed, :afn, :all, ...]

Default Currency

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 config/initializers/money.rb is a very good place to put this.

Currency Exponent

The exponent of a money value is the number of digits after the decimal separator (which separates the major unit from the minor unit). See e.g. ISO 4217 for more information. You can find the exponent (as an Integer) by

Money::Currency.new("USD").exponent  # => 2
Money::Currency.new("JPY").exponent  # => 0
Money::Currency.new("MGA").exponent  # => 1

Currency Lookup

To find a given currency by ISO 4217 numeric code (three digits) you can do

Money::Currency.find_by_iso_numeric(978) #=> Money::Currency.new(:eur)

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

Comparison and arithmetic operations work as expected:

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

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

Exchange rate stores

The default bank is initialized with an in-memory store for exchange rates.

Money.default_bank = Money::Bank::VariableExchange.new(Money::RatesStore::Memory.new)

You can pass your own store implementation, i.e. for storing and retrieving rates off a database, file, cache, etc.

Money.default_bank = Money::Bank::VariableExchange.new(MyCustomStore.new)

Stores must implement the following interface:

# Add new exchange rate.
# @param [String] iso_from Currency ISO code. ex. 'USD'
# @param [String] iso_to Currency ISO code. ex. 'CAD'
# @param [Numeric] rate Exchange rate. ex. 0.0016
#
# @return [Numeric] rate.
def add_rate(iso_from, iso_to, rate); end

# Get rate. Must be idempotent. i.e. adding the same rate must not produce duplicates.
# @param [String] iso_from Currency ISO code. ex. 'USD'
# @param [String] iso_to Currency ISO code. ex. 'CAD'
#
# @return [Numeric] rate.
def get_rate(iso_from, iso_to); end

# Iterate over rate tuples (iso_from, iso_to, rate)
#
# @yieldparam iso_from [String] Currency ISO string.
# @yieldparam iso_to [String] Currency ISO string.
# @yieldparam rate [Numeric] Exchange rate.
#
# @return [Enumerator]
#
# @example
#   store.each_rate do |iso_from, iso_to, rate|
#     puts [iso_from, iso_to, rate].join
#   end
def each_rate(&block); end

# Wrap store operations in a thread-safe transaction
# (or IO or Database transaction, depending on your implementation)
#
# @yield [n] Block that will be wrapped in transaction.
#
# @example
#   store.transaction do
#     store.add_rate('USD', 'CAD', 0.9)
#     store.add_rate('USD', 'CLP', 0.0016)
#   end
def transaction(&block); end

# Serialize store and its content to make Marshal.dump work.
#
# Returns an array with store class and any arguments needed to initialize the store in the current state.

# @return [Array] [class, arg1, arg2]
def marshal_dump; end

The following example implements an ActiveRecord store to save exchange rates to a database.

# rails g model exchange_rate from:string to:string rate:float

class ExchangeRate < ApplicationRecord
  def self.get_rate(from_iso_code, to_iso_code)
    rate = find_by(from: from_iso_code, to: to_iso_code)
    rate&.rate
  end

  def self.add_rate(from_iso_code, to_iso_code, rate)
    exrate = find_or_initialize_by(from: from_iso_code, to: to_iso_code)
    exrate.rate = rate
    exrate.save!
  end

  def self.each_rate
    return find_each unless block_given?

    find_each do |rate|
      yield rate.from, rate.to, rate.rate
    end
  end

  def self.marshal_dump
    [self]
  end
end

The following example implements a Redis store to save exchange rates to a redis database.

class RedisRateStore
  INDEX_KEY_SEPARATOR = '_TO_'.freeze

  # Using second db of the redis instance
  # because sidekiq uses the first db
  REDIS_DATABASE = 1

  # Using Hash to store rates data
  REDIS_STORE_KEY = 'rates'

  def initialize
    conn_url = "#{Rails.application.credentials.redis_server}/#{REDIS_DATABASE}"
    @connection = Redis.new(url: conn_url)
  end

  def add_rate(iso_from, iso_to, rate)
    @connection.hset(REDIS_STORE_KEY, rate_key_for(iso_from, iso_to), rate)
  end

  def get_rate(iso_from, iso_to)
    @connection.hget(REDIS_STORE_KEY, rate_key_for(iso_from, iso_to))
  end

  def each_rate
    rates = @connection.hgetall(REDIS_STORE_KEY)
    return to_enum(:each_rate) unless block_given?

    rates.each do |key, rate|
      iso_from, iso_to = key.split(INDEX_KEY_SEPARATOR)
      yield iso_from, iso_to, rate
    end
  end

  def transaction
    yield
  end

  private

  def rate_key_for(iso_from, iso_to)
    [iso_from, iso_to].join(INDEX_KEY_SEPARATOR).upcase
  end
end

Now you can use it with the default bank.

# For Rails 6 pass model name as a string to make it compatible with zeitwerk
# Money.default_bank = Money::Bank::VariableExchange.new("ExchangeRate")
Money.default_bank = Money::Bank::VariableExchange.new(ExchangeRate)

# Add to the underlying store
Money.default_bank.add_rate('USD', 'CAD', 0.9)
# Retrieve from the underlying store
Money.default_bank.get_rate('USD', 'CAD') # => 0.9
# Exchanging amounts just works.
Money.from_cents(1000, 'USD').exchange_to('CAD') #=> #<Money fractional:900 currency:CAD>

There is nothing stopping you from creating store objects which scrapes XE for the current rates or just returns rand(2):

Money.default_bank = Money::Bank::VariableExchange.new(StoreWhichScrapesXeDotCom.new)

You can also implement your own Bank to calculate exchanges differently. Different banks can share Stores.

Money.default_bank = MyCustomBank.new(Money::RatesStore::Memory.new)

If you wish to disable automatic currency conversion to prevent arithmetic when currencies don't match:

Money.disallow_currency_conversion!

Implementations

The following is a list of Money.gem compatible currency exchange rate implementations.

Formatting

There are several formatting rules for when Money#format is called. For more information, check out the formatting module source, or read the latest release's rdoc version.

If you wish to format money according to the EU's Rules for expressing monetary units in either English, Irish, Latvian or Maltese:

m = Money.from_cents('123', :gbp) # => #<Money fractional:123 currency:GBP>
m.format(symbol: m.currency.to_s + ' ') # => "GBP 1.23"

Rounding

By default, Money objects are rounded to the nearest cent and the additional precision is not preserved:

Money.from_amount(2.34567).format #=> "$2.35"

To retain the additional precision, you will also need to set infinite_precision to true.

Money.default_infinite_precision = true
Money.from_amount(2.34567).format #=> "$2.34567"

To round to the nearest cent (or anything more precise), you can use the round method. However, note that the round method on a Money object does not work the same way as a normal Ruby Float object. Money's round method accepts different arguments. The first argument to the round method is the rounding mode, while the second argument is the level of precision relative to the cent.

# Float
2.34567.round     #=> 2
2.34567.round(2)  #=> 2.35

# Money
Money.default_infinite_precision = true
Money.from_cents(2.34567).format       #=> "$0.0234567"
Money.from_cents(2.34567).round.format #=> "$0.02"
Money.from_cents(2.34567).round(BigDecimal::ROUND_HALF_UP, 2).format #=> "$0.0235"

You can set the default rounding mode by passing one of the BigDecimal mode enumerables like so:

Money.rounding_mode = BigDecimal::ROUND_HALF_EVEN

See BigDecimal::ROUND_MODE for more information

Ruby on Rails

To integrate money in a Rails application use money-rails.

For deprecated methods of integrating with Rails, check the wiki.

Localization

In order to localize formatting you can use I18n gem:

Money.locale_backend = :i18n

With this enabled a thousands seperator and a decimal mark will get looked up in your I18n translation files. In a Rails application this may look like:

# config/locale/en.yml
en:
  number:
    currency:
      format:
        delimiter: ","
        separator: "."
  # falling back to
  number:
    format:
      delimiter: ","
      separator: "."

For this example Money.from_cents(123456789, "SEK").format will return 1,234,567.89 kr which otherwise would have returned 1 234 567,89 kr.

This will work seamlessly with rails-i18n gem that already has a lot of locales defined.

If you wish to disable this feature and use defaults instead:

Money.locale_backend = nil

Deprecation

The current default behaviour always checks the I18n locale first, falling back to "per currency" localization. This is now deprecated and will be removed in favour of explicitly defined behaviour in the next major release.

If you would like to use I18n localization (formatting depends on the locale):

Money.locale_backend = :i18n

# example (using default localization from rails-i18n):
I18n.locale = :en
Money.from_cents(10_000_00, 'USD').format # => $10,000.00
Money.from_cents(10_000_00, 'EUR').format # => €10,000.00

I18n.locale = :es
Money.from_cents(10_000_00, 'USD').format # => $10.000,00
Money.from_cents(10_000_00, 'EUR').format # => €10.000,00

If you need to localize the position of the currency symbol, you have to pass it manually. Note: this will become the default formatting behavior in the next version.

I18n.locale = :fr
format = I18n.t :format, scope: 'number.currency.format'
Money.from_cents(10_00, 'EUR').format(format: format) # => 10,00 €

For the legacy behaviour of "per currency" localization (formatting depends only on currency):

Money.locale_backend = :currency

# example:
Money.from_cents(10_000_00, 'USD').format # => $10,000.00
Money.from_cents(10_000_00, 'EUR').format # => €10.000,00

In case you don't need localization and would like to use default values (can be redefined using Money.default_formatting_rules):

Money.locale_backend = nil

# example:
Money.from_cents(10_000_00, 'USD').format # => $10000.00
Money.from_cents(10_000_00, 'EUR').format # => €10000.00

Collection

In case you're working with collections of Money instances, have a look at money-collection for improved performance and accuracy.

Troubleshooting

If you don't have some locale and don't want to get a runtime error such as:

I18n::InvalidLocale: :en is not a valid locale

Set the following:

I18n.enforce_available_locales = false

Heuristics

Prior to v6.9.0 heuristic analysis of string input was part of this gem. Since then it was extracted in to money-heuristics gem.

Migration Notes

Version 6.0.0

The Money#dollars and Money#amount methods now return instances of BigDecimal rather than Float. We should avoid representing monetary values with floating point types so to avoid a whole class of errors relating to lack of precision. There are two migration options for this change:
- The first is to test your application and where applicable update the application to accept a BigDecimal return value. This is the recommended path.
- The second is to migrate from the #amount and #dollars methods to use the #to_f method instead. This option should only be used where Float is the desired type and nothing else will do for your application's requirements.

money

Development

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