fastapi-backend-guidelines

Structure your FastAPI project using a three-layer architecture (Router → Service → Repository) combined with domain-driven design to organize code by domain modules, prevent concern leakage, and ensure testability.

The best way to separate read and write sessions in an async FastAPI backend is to apply a read/write session split pattern across your repository layer, which optimizes database interactions and ensures transactional safety.

Handle data validation and business rules in FastAPI services by using Pydantic DTOs with field_validator to enforce data integrity, combined with domain-exception-based error handling for robust validation.

Yes, you can implement ULID-based ID generation with domain prefixes in FastAPI to create readable, sortable identifiers across your service and repository layers instead of standard UUIDs.

FastAPI works exceptionally well with async/await patterns throughout the entire stack, allowing you to maximize performance and scalability across routers, services, and repositories.

Prevent logic leakage by enforcing a strict three-layer architecture (Router → Service → Repository) with clear responsibilities, ensuring API routes handle requests while repositories manage data access.