Dependency Injection Wiring

Dependency Injection Wiring

Prerequisites & Dependencies

• TypeScript 5+ (recommended) or Python 3.10+
• Understanding of interfaces and inversion of control principles
• Optional: npm i inversify / pip i dependency-injector or manual DI container

Execution Steps

1. Define interfaces for all high-level dependencies (database, email service, external APIs)
2. Create concrete implementations of those interfaces
3. Build a DI container (or use an existing one) that maps interfaces → implementations
4. Request dependencies via constructor injection or property injection, avoid new or global singletons in business logic
5. Wire the container at the application bootstrap (e.g., index.ts, main.py) and verify that swapping implementations (mock vs real) is trivial for testing
6. Document the DI graph and ensure no circular dependencies exist

// InversifyJS example: interface → implementation wiring
import { injectable, inject, interfaces } from 'inversify';
import { TYPES } from './types';

@injectable()
class UserService {
  constructor(@inject(TYPES.IUserRepository) private repo: IUserRepository) {}
  async getById(id: string) { return this.repo.find(id); }
}

@injectable()
class UserRepository implements IUserRepository {
  async find(id: string) { /* DB logic */ }
}

const container = new Container();
container.bind<IUserRepository>(TYPES.IUserRepository).to(UserRepository);

// Bootstrap app with resolved dependencies
const service = container.get(UserService);
service.getById('123');