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💼 Payroll System – API for Small Business Management

📖 Overview and Context

The project involved developing a payroll management API from scratch for small businesses. The goal was to build a modular, scalable, and modern solution capable of adapting to different business structures and legal requirements.

During my participation, I contributed to the initial database design, leveraging my accounting background, and collaborated on defining the core system architecture, based on Hexagonal Architecture and Vertical Slice principles, implemented using FastAPI (Python).

👤 Role and Contribution

  • Main Role: Backend Developer
  • Key Contributions:
  • Designed the initial database schema for the payroll module.
  • Implemented CRUD endpoints for companies and job profiles.
  • Collaborated with another developer to define the system’s architecture.
  • Reviewed and structured the project to ensure layer independence and scalability.

🛠️ Tech Stack

  • Language: Python 3
  • Framework: FastAPI
  • Database: PostgreSQL
  • Architecture: Hexagonal + Vertical Slice
  • ORM: SQLAlchemy
  • Other Tools: Pydantic, Alembic (migrations), Uvicorn

🧭 System Architecture

The following diagram illustrates the overall structure of the API, highlighting its modular design and data flow based on Hexagonal Architecture.

graph TD
  subgraph Domain Layer
    E[Entities]
    U[Use Cases]
  end

  subgraph Application Layer
    S[Services / Business Logic]
  end

  subgraph Infrastructure Layer
    DB[(PostgreSQL)]
    R[FastAPI Routers]
    M[Alembic Migrations]
  end

  R --> S
  S --> U
  U --> E
  S --> DB
  M --> DB

📡 Example of Implemented Endpoint

@router.post("/", response_model=CompanyOut)
async def create_company(company_data: CreateCompanyRequest, use_case: CompanyUseCases = Depends(get_company_use_cases)):
    return use_case.create_company(company_data)

🚀 Achievements and Learnings

  • Contributed to the foundation of the system, ensuring compliance with accounting requirements and scalability for future integrations.
  • Quickly mastered the FastAPI stack and its modern concepts (dependency injection, routers, Pydantic schemas).
  • Implemented the first functional modules (companies and job profiles), serving as a reference for future development.
  • Deepened my understanding of design patterns, hexagonal architecture, and separation of concerns.

🧭 Personal Reflection

This project was a technical and adaptive challenge — it required learning a new framework and applying advanced architectural concepts while laying the groundwork for a real-world product.
The experience strengthened my ability to quickly learn new technologies, collaborate on clean architectural designs, and align software development with accounting and business principles.