generating-fastapi-domains

FastAPI Domain Generator

When to use this skill

• When starting a new backend feature that requires its own domain model.
• When expanding the backend with new business entities and logic.
• Use when the user requests "create a new domain", "scaffold a backend feature", or "setup hexagonal structure for [X]".

Workflow

1. Define Domain Name: Identify the singular name of the domain (e.g., incident, news, member).
2. Create Directory Structure: Ensure the following hierarchy exists under backend/app/:
   • application/use_cases/[domain_name_plural]/
   • domain/entities/
   • domain/repositories/
   • infrastructure/db/mappers/
   • infrastructure/models/
   • infrastructure/repositories/
   • presentation/api/
   • presentation/schemas/
3. Generate Foundation Files: Create base boilerplate for each layer (see Templates).
4. Register Router: Add the new domain router to the main FastAPI application in backend/app/main.py.
5. Verify DoD: Ensure the new structure complies with @/.agent/rules/techstack-backend.md.

Directory Checklist

• backend/app/domain/entities/[domain_name].py
• backend/app/domain/repositories/[domain_name]_repository.py
• backend/app/application/use_cases/[domain_name_plural]/__init__.py
• backend/app/infrastructure/models/[domain_name].py
• backend/app/infrastructure/db/mappers/[domain_name]_mapper.py
• backend/app/infrastructure/repositories/[domain_name]_repository_impl.py
• backend/app/presentation/api/[domain_name_plural].py
• backend/app/presentation/schemas/[domain_name].py

Instructions

1. Entity Pattern

Entities MUST be plain Python classes or Dataclasses, independent of any framework. Use type hints for all attributes.

2. Repository Interface

Define an abstract base class (ABC) in the domain layer. This defines the "Port".

3. Infrastructure Implementation

The database model (SQLAlchemy) and the repository implementation (Adapter) live in the infrastructure layer.

4. Presentation & Schemas

Use Pydantic V2 for schemas. Ensure routers only call Use Cases, never repositories directly.

Resources

Templates for these files can be found in @/.agent/skills/fastapi-domain-generator/resources/ (if available).