Jyjeanne AI Setup Forge Clean Architecture Node

Purpose

To decouple business logic from frameworks, databases, and external tools, making the application easier to test and maintain over time.

When to Use

• When building complex enterprise applications.
• When you want to ensure the business logic can survive changes in the database (e.g., SQL to NoSQL) or framework (e.g., Express to NestJS).
• When you need high testability of core business rules.

Procedure

1. Structure the Directory (Layers)

Organize the code into four distinct layers:

• Entities: Enterprise business rules (Plain objects/classes).
• Use Cases: Application-specific business rules.
• Interface Adapters: Controllers, Gateways, Presenters.
• Frameworks & Drivers: Express, TypeORM, External APIs.

2. Implementation: The Entity

// src/domain/entities/User.ts
export class User {
  constructor(
    public readonly id: string,
    public readonly email: string,
    public readonly passwordHash: string
  ) {}

  public validateEmail() {
    return this.email.includes('@');
  }
}

3. Implementation: The Use Case

Use cases should only depend on abstractions (interfaces).

// src/application/use-cases/CreateUser.ts
import { User } from '../../domain/entities/User';

export interface UserRepository {
  save(user: User): Promise<void>;
  findByEmail(email: string): Promise<User | null>;
}

export class CreateUser {
  constructor(private userRepository: UserRepository) {}

  async execute(data: any) {
    const user = new User(Date.now().toString(), data.email, data.password);
    if (!user.validateEmail()) throw new Error('Invalid email');
    
    await this.userRepository.save(user);
  }
}

4. Implementation: The Adapter (Repository)

Implement the interface defined in the application layer.

// src/infrastructure/repositories/SqlUserRepository.ts
import { UserRepository } from '../../application/use-cases/CreateUser';
import { User } from '../../domain/entities/User';

export class SqlUserRepository implements UserRepository {
  async save(user: User): Promise<void> {
    // DB logic using Prisma/TypeORM
  }
  
  async findByEmail(email: string): Promise<User | null> {
    // DB logic
    return null;
  }
}

5. Dependency Injection

Wire everything together in the outermost layer.

// src/main.ts
const userRepository = new SqlUserRepository();
const createUserUseCase = new CreateUser(userRepository);
const userController = new UserController(createUserUseCase);

Constraints

• Dependency Rule: Dependencies must only point inwards (Infrastructure -> Application -> Domain).
• No Frameworks in Domain: Domain entities should be pure TypeScript/JavaScript.
• Testing: Use cases should be tested with mocks of the repositories.

Expected Output

A decoupled codebase where the core logic is independent of the UI and Database choices.

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