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Multi-Currency

🌐 Overview

The fintech platform supports multi-currency accounts and transactions with robust, precise, and domain-driven conversion and rounding logic. All currency conversion and rounding is handled in the domain layer, ensuring:

  • Any float64 value can be safely converted and stored.
  • Rounding is always performed to the correct number of decimals for the target currency using big.Rat.
  • The domain layer is responsible for all rounding and validation, not the service or API layers.

How It Works

  • Users can deposit, withdraw, and transfer in any supported currency.
  • The system fetches real-time exchange rates and performs conversion in the domain layer.
  • The result is rounded to the correct number of decimals for the target currency.
  • All values are stored in the smallest unit (e.g., cents for USD) as BIGINT.
  • Conversion details (original amount, rate, etc.) are stored as DECIMAL(30,15) for full float64 compatibility.

🗄️ Database Schema

  • Money values: BIGINT (smallest unit)
  • Conversion fields: DECIMAL(30,15)

🏅 Best Practices

  • Pass raw float64 values to the domain layer; do not round in the service or API layers.
  • The domain will round and validate as needed.
  • All conversion and rounding logic is centralized for consistency and safety.

🧪 Example

  • Deposit 1,000,000,000 JPY to a USD account:
  • The system fetches the exchange rate, converts, and rounds to 2 decimals for USD.
  • The result is stored as an integer (cents) in the DB.
  • The original amount, rate, and conversion details are stored as DECIMAL(30,15).

🚀 Recent Improvements

  • Domain-driven rounding and validation using big.Rat
  • Full float64 compatibility for conversion fields
  • DB schema updated for DECIMAL(30,15) on conversion fields
  • All overflow and decimal errors are now handled before DB writes