Xrate

Xrate is a gem for Rails which provides historic exchange rate lookups against a base currency.

This gem uses the European Central Bank 90 day historic rate feed as a source, but other sources can be used by storing the rates by creating Rate objects:

Xrate:Rate.create(date: Date.today, currency: "GBP", rate: 0.555)

Xrate will raise an exception if the conversion cannot be carried out due to lack of data. You should plan to gracefully handle Xrate::UnconvertableCurrencyExceptions in your app.

Add this line to your application's Gemfile:

gem "xrate"

And then execute:

$ bundle

Xrate assumes that all rates will be against a base currency defined in the environment variable XRATE_BASE_CURRENCY, for example "EUR".

Exchange rate datasets will often have missing data, due to market closures (e.g. weekends and religious/national holidays). To handle this, Xrate will fall back to the last available datapoint, within a given number of days. This fallback range must be provided in the environment variable XRATE_FALLBACK_DAYS. A sensible default for this is 4, as this will cover Easter and any Christmas that spans a weekend. You can increase/decrease this depending on the dataset and the accuracy your application requires.

Xrate stores a cache of the current exchange rates in the database and assumes ActiveRecord is present. To generate the migration for this table, run rails generate xrate:install and rails db:migrate to run the migration.

To get the last 90 days of exchange rate data from the European Central Bank, run rake xrate:import. This can be run on a regular basis to keep your rate cache up to date. Note, Xrate will always take the last import as correct, overwriting any previous stored rates.

Lookups are made by running Xrate::ExchangeRate.at({Date:date}, {String:source_currency}, {String:target_currency})

To find out the how much £1 was worth in USD the day before brexit, you would run:

Xrate::ExchangeRate.at("2016-06-22", "GBP", "USD")

Xrate returns rates in BigDecimal.

• Add caching layer to prevent the need to hit the database for each lookup
• Make ORM and framework-agnostic

Bug reports and pull requests are welcome on GitHub at https://github.com/samward/xrate.

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