ddd_wallet

DDD Wallet Example

A small Domain-Driven Design sample built with the Vania framework. A wallet you can open, deposit into, and withdraw from — used to show the DDD layering, not the money math.

Layers

The dependency rule points inward: outer layers depend on inner ones, never the reverse.

lib/
  domain/                     # the core — pure Dart, no framework
    money.dart                #   value object (immutable, never negative)
    wallet.dart               #   aggregate root (guards its own invariants)
    wallet_repository.dart    #   repository interface (owned by the domain)
    wallet_exception.dart     #   domain error
  application/
    wallet_service.dart       # use-case orchestration (no business rules)
  infrastructure/
    in_memory_wallet_repository.dart  # concrete repository implementation
  interface/http/
    wallet_controller.dart    # HTTP adapter + composition root
    wallet_route.dart         # routes
  app/providers/ , config/    # framework wiring
bin/server.dart
test/                         # domain + application tests

The ideas it demonstrates

• Value object — Money is immutable, compared by value, and enforces "never negative" in its own constructor.
• Aggregate root — Wallet exposes behaviour (deposit, withdraw), not setters; the balance can never go below zero or change from outside.
• Repository interface in the domain, implemented in infrastructure, so the application layer depends on an abstraction — swap the in-memory store for a database without touching the domain.
• Application service orchestrates a use case (load → act → save) and holds no rules of its own.
• Thin HTTP layer — the controller only maps requests/responses and turns domain errors into status codes.

Endpoints

Method	Path	Description
POST	/api/wallets/{id}	Open a wallet
GET	/api/wallets/{id}	Show the balance
POST	/api/wallets/{id}/deposit	Deposit cents
POST	/api/wallets/{id}/withdraw	Withdraw cents

Running

dart pub get
dart run bin/server.dart

Tests

The domain and application layers are pure Dart, so they test without a server or database:

dart test