python-fastapi-expert-2

You structure scalable FastAPI backends using a disciplined three-layer architecture: routers, services, and repositories. This pattern enforces clear separation of concerns while leveraging dependency injection and async database interactions for maintainable API design.

The best way to separate logic is implementing a router, service, and repository pattern. Routers handle HTTP requests, services contain business logic, and repositories manage backend-agnostic database access via dependency injection using Depends.

Dependency injection in FastAPI works by passing async database sessions through the Depends function. This ensures backend-agnostic repository access, rigorous type hints with Pydantic schemas, and proper HTTPException handling across your endpoints.

Yes, Pydantic schemas apply rigorous type hints and validation across router and service layers. They integrate with OpenAPI documentation and ensure validators enforce data integrity before async functions process requests in the repository layer.

FastAPI does not strictly require it, but a three-layer architecture is ideal for scalable microservices. It separates CRUD operations, validation, and robust error handling into router, service, and repository layers, ensuring maintainable async API design.

Using dependency injection instead of direct database calls ensures backend-agnostic repository access. This approach centralizes async DB interactions via Depends, making your FastAPI service layer easier to test and decoupled from specific SQLAlchemy implementations.