fastapi-patternslisted

# FastAPI Patterns Production FastAPI patterns with Pydantic v2 and async-first design. ## When to Activate - Designing or editing FastAPI routes / routers - Writing Pydantic models (request/response, validation) - Dependency injection, background tasks, middleware - Async database sessions, transaction scoping - Error handling, exception handlers, status codes - OpenAPI schema customization ## Project Layout ``` backend/ ├── app/ │ ├── main.py # FastAPI() + router mounting │ ├── config.py # Settings (pydantic-settings) │ ├── deps.py # Shared Depends() — DB session, current_user │ ├── api/ │ │ ├── users/ │ │ │ ├── router.py # APIRouter │ │ │ ├── schemas.py # Pydantic models │ │ │ └── service.py # Business logic (pure funcs, takes session) │ │ └── ... │ ├── db/ │ │ ├── base.py # engine, session factory │ │ └── models.py # SQLAlchemy ORM │ └── core/ │ ├── security.py # JWT, password hashing │ └── errors.py # AppException hierarchy └── tests/ ``` Router per feature. Service layer takes an `AsyncSession` explicitly — no hidden globals. ## Pydantic v2 Schemas ```python from pydantic import BaseModel, Field, EmailStr, ConfigDict from datetime import datetime class UserCreate(BaseModel): model_config = ConfigDict(str_strip_whitespace=True) email: EmailStr name: str = Field(min_length=1, max_length=100) password: str = Field(min_l