ActiveCurrency

Rails plugin to retrieve and store the currency rates daily to integrate with the money-rails gem.

Rationale

Storing the current currency rates in the database using ActiveCurrency provides the following advantages:

• Lets you query for the currency rate you actually used in your application at any given time.
• Does not need to call an API to get the rates when starting or restarting your web server.
• Does not depend on the file system to store cached rates.
• Choose how often you want to update the currency rates (daily for example).
• Your users do not suffer the cost of making calls to the bank rates API.
• Your app does not go down when the bank rates API does.

To fetch the current rate it uses your application cache instead of making a call to the database.

Usage

Store the current rate regularly by calling in a scheduled job (using something like sidekiq-scheduler, whenever, or active_scheduler) with the currencies you want to store:

ActiveCurrency::AddRates.call(%w[EUR USD])

You can then exchange money by using the Money gem helpers:

10.to_money('EUR').exchange_to('USD').cents

If you need to look up the previous currency rates:

ActiveCurrency::Rate.value_for('EUR', 'USD', 1.month.ago)
# => 1.151
ActiveCurrency::Rate.where(from: 'EUR', to: 'USD').pluck(:value)
# => [1.162, 1.162, 1.161, 1.161, 1.163, …]

Installation

Add these lines to your application's Gemfile:

# Store and retrieve the currency from the database.
gem 'active_currency'

And in config/initializers/money.rb:

MoneyRails.configure do |config|
  config.default_bank = ActiveCurrency::Bank.new
end

Then call bin/rake db:migrate to create the table that holds the currency rates and fill it for the first time.

Fetching rates

By defaut it uses the eu_central_bank to update the currency rates.

If you prefer another API, you can provide any Money-compatible bank when calling ActiveCurrency::AddRates. For example with the money-open-exchange-rates gem:

require 'money/bank/open_exchange_rates_bank'

bank = Money::Bank::OpenExchangeRatesBank.new(Money::RatesStore::Memory.new)
bank.app_id = '…'

ActiveCurrency::AddRates.call(%w[EUR USD], bank: bank)

The first currency you give to AddRates is considered the default currency against which other currency rates will be guessed if they are unavailable.

Tests

In your app test suite you may not want to have to fill your database to be able to exchange currencies.

For that, you can use a fake rate store in your rails_helper.rb:

MoneyRails.configure do |config|
  rate_store = Money::RatesStore::Memory.new.tap do |store|
    store.add_rate('USD', 'EUR', 1.5)
    store.add_rate('EUR', 'USD', 1.4)
  end
  config.default_bank = Money::Bank::VariableExchange.new(rate_store)
end

Contributing

Please file issues and pull requests on GitHub.

Development

Install:

BUNDLE_GEMFILE=Gemfile-rails6.0 bundle install

Launch specs and linters:

BUNDLE_GEMFILE=Gemfile-rails6.0 bin/rake

Release

Update CHANGELOG.md, update version in lib/active_currency/version.rb.

Then:

gem install bundler:1.17.2
BUNDLE_GEMFILE=Gemfile-rails4.2 bundle update
BUNDLE_GEMFILE=Gemfile-rails5.2 bundle update

gem install bundler:2.1.2
BUNDLE_GEMFILE=Gemfile-rails6.0 bundle update

git add CHANGELOG.md lib/active_currency/version.rb Gemfile-rails*.lock
git commit -m v`ruby -r./lib/active_currency/version <<< 'puts ActiveCurrency::VERSION'`
bin/rake release

License

The gem is available as open source under the terms of the MIT License.