303-fastapi

What problem does it solve?

It solves the challenge of building production-grade FastAPI backends reliably by enforcing a clean Service Layer architecture, correct async/sync concurrency behavior, and consistent error handling that keeps business logic independent from HTTP concerns.

Core Features & Use Cases

• Service Layer Pattern by design: Separates Transport (FastAPI routers/controllers) from Business Logic (services) so your rules remain testable and stable.
• Pydantic v2 validation & schema rigor: Encourages explicit request/response models to reduce runtime contract drift.
• Async/sync concurrency matrix: Provides clear rules for async I/O, sync I/O via FastAPI’s threadpool, and CPU-bound work via process offloading.
• Testability-first approach: Promotes unit testing with TestClient, dependency_overrides, and fixture-based cleanup to prevent cross-test leakage.
• Use Case: You’re developing a REST API for a trading data service and need endpoints that validate input with Pydantic, delegate logic to services, map service exceptions to correct HTTP responses, and stay reliable under high-concurrency traffic.

Quick Start

Ask the AI to scaffold a FastAPI app using the Service Layer pattern, add Pydantic v2 request/response models, implement global exception mapping for service errors, and generate unit tests using TestClient with dependency overrides.