Question

I’m using the Ruby Money gem in a multi-tenant (SaaS) Rails app, and am looking for a good way to make the Money.default_currency be set to an Account’s preference for each request. I have several currency-related models in the app that use the Money class.

I have everything working properly in development, but I’m just looking for some feedback on whether or not the solution with have repercussions in production.

Here’s what I did in my ApplicationController (irrelevant code removed for brevity):

class ApplicationController < ActionController::Base
  before_filter :set_currency

  private

  def set_currency
    Money.default_currency = Money::Currency.new(current_account.present? && current_account.currency.present? ?
                                                 current_account.currency : 'USD')
  end
end

So the code above will set the default_currency class variable to the current account’s preference, or default back to ‘USD’ if there isn’t one.

By the way, here’s the relevant default_currency code in the Money class:

class Money

  # Class Methods
  class << self

    # The default currency, which is used when +Money.new+ is called without an
    # explicit currency argument. The default value is Currency.new("USD"). The
    # value must be a valid +Money::Currency+ instance.
    #
    # @return [Money::Currency]
    attr_accessor :default_currency

  end
end

So, will this work as expected in a multi-user setting? Anything else I need to do?

Answer 1

Most rails apps don’t run in multithreaded mode – a given instance is only ever handling one request at a time (this is the default).

If your app was in multithreaded mode this would be dangerous – Money.default_currency could get changed halfway through a request by the new request that has just come in. If you did want to make this thread safe, you could use the Thread.current hash to have per thread values of default_currency