fastapi-layered-architecture

To separate business logic from SQL queries in FastAPI, enforce a layered architecture where the Service layer handles business logic and coordinates commits, while the Repository layer builds SQL queries and returns model instances. This strict separation prevents tangled code and ensures endpoints do not mix concerns.

The best way to structure a production FastAPI project is using a strict Layered Architecture with separate directories for api/endpoints, services, repositories, models, and schemas. This enforces clear boundaries between Router, Service, and Repository layers for maintainability.

FastAPI endpoints mix request parsing with database operations when a strict layered architecture is not enforced. By delegating request parsing and Pydantic validation to the Router, business logic to the Service, and SQL queries to the Repository, you establish clear boundaries and eliminate tangled code.

You do not need external tools to enforce layered architecture in FastAPI. This approach requires no external tooling beyond standard Python FastAPI practices, relying entirely on structural separation into Router, Service, and Repository layers to guide teams toward maintainability.

You can refactor an existing FastAPI app to use Router, Service, and Repository layers. This Skill applies to refactors where endpoints mix concerns, guiding teams toward clear boundaries by specifying responsibilities for parsing requests, implementing business logic, and building SQL queries.