Amountable

This gem helps you integrate Money fields into your ActiveRecord models without having to add new columns each time.

It also helps manage and sum various components of your models to keep amount definitions consistent across your application.

Installation

Add

gem 'amountable', github: 'instacart/amountable'

to your Gemfile. Then run

bundle

and

rake amountable:install:migrations

and finally

rake db:migrate

Usage

Setup your model

class Order < ActiveRecord::Base
  include Amountable
  amount :subtotal, sets: [:total]
  amount :delivery_fee, sets: [:total, :fees]
  amount :bags_fee, sets: [:total, :fees]
  amount :sales_tax, sets: [:total, :taxes]
  amount :local_tax, sets: [:total, :taxes]
end

then create it

order = Order.create(
  subtotal: Money.new(123),
  delivery_fee: Money.new(100),
  bags_fee: Money.new(10),
  sales_tax: Money.new(56)
  )
order.subtotal
# => #<Money fractional:123 currency:USD>
order.total
# => #<Money fractional:289 currency:USD>
order.fees
# => #<Money fractional:110 currency:USD>
order.taxes
# => #<Money fractional:56 currency:USD>

Implementation

When you run the migration, an amounts table will be created with a polymorphic relationship to an amountable, which in the above example would be your orders.

When the an order is created with some amounts, the associated Amount objects are persisted.

Amount objects are persisted in bulk, so there are no N + 1 queries. If an amount is zero, no Amount model is created.