What Is Clean Architecture?

Clean Architecture organizes code into independent layers. Makes applications testable, maintainable, and adaptable to change.

The Layers

Entities      = Business Objects (core, most independent)
Use Cases     = Application Logic
Controllers   = Interface Adapters
Frameworks    = External (DB, Web, etc.)

Entity Example

// entities/User.ts
class User {
  constructor(
    public readonly id: string,
    public name: string,
    public email: string
  ) {}
  
  changeName(newName: string): void {
    if (!newName.trim()) throw new Error('Invalid name');
    this.name = newName;
  }
}

Use Case Example

// useCases/CreateUser.ts
interface UserRepository {
  save(user: User): Promise;
  findByEmail(email: string): Promise;
}

class CreateUserUseCase {
  constructor(private userRepo: UserRepository) {}
  
  async execute(data: CreateUserDTO): Promise {
    const existing = await this.userRepo.findByEmail(data.email);
    if (existing) throw new Error('Email exists');
    
    const user = new User(uuid(), data.name, data.email);
    await this.userRepo.save(user);
    return user;
  }
}

Dependency Rule

Dependencies point inward only. Entities know nothing about outer layers. This isolation enables flexibility and testing.

Conclusion

Clean Architecture is an investment for long-term projects. The structure enables adaptability as requirements evolve.