Fastapi Patterns

# FastAPI Patterns

Production-oriented patterns for FastAPI services.

## When to Use

- Building or reviewing a FastAPI app.
- Splitting routers, schemas, dependencies, and database access.
- Writing async endpoints that call a database or external service.
- Adding authentication, authorization, OpenAPI docs, tests, or deployment settings.
- Checking a FastAPI PR for copy-pasteable examples and production risks.

## How It Works

Treat the FastAPI app as a thin HTTP layer over explicit dependencies and service code:

- `main.py` owns app construction, middleware, exception handlers, and router registration.
- `schemas/` owns Pydantic request and response models.
- `dependencies.py` owns database, auth, pagination, and request-scoped dependencies.
- `services/` or `crud/` owns business and persistence operations.
- `tests/` overrides dependencies instead of opening production resources.

Prefer small routers and explicit `response_model` declarations. Keep raw ORM objects, secrets, and framework globals out of response schemas.

## Project Layout

```text
app/
|-- main.py
|-- config.py
|-- dependencies.py
|-- exceptions.py
|-- api/
|   `-- routes/
|       |-- users.py
|       `-- health.py
|-- core/
|   |-- security.py
|   `-- middleware.py
|-- db/
|   |-- session.py
|   `-- crud.py
|-- models/
|-- schemas/
`-- tests/
```

## Application Factory

Use a factory so tests and workers can build the app with controlled settings.