WhittakerTech::Midas

Midas is a Rails engine for elegant, multi-currency monetary value management.

Instead of adding price_cents and price_currency columns to every model that needs money, Midas stores all monetary values in a single polymorphic Coin ledger. The Bankable concern gives any ActiveRecord model a clean DSL for declaring and accessing its monetary attributes.

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Key capabilities

• Single canonical ledger — one wt_midas_coins table for every monetary value across your entire application
• Declarative DSL — has_coin :price / has_coins :subtotal, :tax, :total
• Exact arithmetic — integer minor-unit math, no floating-point errors
• Flexible input coercion — accepts Money objects, floats, integers, and strings
• Token-based formatting — strftime-like grammar for custom display strings
• RTL support — Unicode bidirectional isolation for Arabic and Hebrew UIs
• Per-unit pricing — Allocation value object for per-unit / bulk pricing
• Bank-style currency input — Stimulus controller with automatic decimal handling
• 90%+ test coverage

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Requirements

Requirement	Version
Ruby	>= 3.4
Rails	>= 7.1
money gem	~> 6.19

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Quick look

class Invoice < ApplicationRecord
  include WhittakerTech::Midas::Bankable

  has_coins :subtotal, :tax, :total
end

invoice = Invoice.create!
invoice.set_subtotal(amount: 100.00, currency_code: 'USD')
invoice.set_tax(amount: 8.50,  currency_code: 'USD')
invoice.set_total(amount: 108.50, currency_code: 'USD')

invoice.subtotal_format   # => "$100.00"
invoice.tax_amount        # => #<Money @fractional=850 @currency="USD">
invoice.total             # => #<WhittakerTech::Midas::Coin ...>

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Documentation sections

• Installation — add the gem, run migrations, register the Stimulus controller
• Usage — Bankable DSL, Coin arithmetic, Presenter, Allocation
• Architecture — design decisions, module breakdown, schema
• API Reference — full method reference; generated API docs at api/WhittakerTech/Midas.md
• Examples — e-commerce products, invoicing, bulk pricing, RTL display

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Why Midas?

Monetary code is some of the most fragile code in a Rails application. Rounding errors, currency mismatches, and schema duplication accumulate quietly until a financial report or a refund exposes them.

Midas makes the single-ledger approach — standard in accounting software — the default for Rails. One table, one set of rules, one place to add audit hooks or exchange rate logic.