api-endpoint

API Endpoint

Scaffold one new endpoint across the layers the project already uses. Don't invent a layer the codebase doesn't have.

Steps

1. Ask once (if not already specified): method + path (e.g. POST /users), what it does, and the response shape. Do not guess.
2. Read a sibling endpoint in app/api/ (or the project's equivalent) to match: router setup, dependency injection, error handling, test file layout. If no sibling exists, use the shape below.
3. Create or edit these files, in order:
   • app/schemas/<resource>.py — request + response Pydantic models. If the file exists, add the new models; do not rewrite it.
   • app/services/<resource>.py — the pure-ish function that does the work. No request/response handling here.
   • app/api/<resource>.py — the route handler. Call the service, map domain exceptions to HTTP codes.
   • tests/api/test_<resource>.py — one happy-path test and one failure test (invalid input → 422, or domain error → mapped status).
4. Register the router in app/api/__init__.py (or the project's equivalent) only if adding a new resource file.
5. Run ruff format and ruff check on the files you touched. Report any remaining lint errors; do not auto-fix mypy errors without showing the user the diff.

Default shape (FastAPI)

# app/schemas/widget.py
from pydantic import BaseModel, Field

class WidgetCreate(BaseModel):
    name: str = Field(min_length=1, max_length=80)

class WidgetOut(BaseModel):
    id: int
    name: str

# app/services/widgets.py
from app.schemas.widget import WidgetCreate, WidgetOut

def create_widget(db, payload: WidgetCreate) -> WidgetOut:
    widget = Widget(name=payload.name)
    db.add(widget); db.flush()
    return WidgetOut(id=widget.id, name=widget.name)

# app/api/widgets.py
from fastapi import APIRouter, Depends
from app.schemas.widget import WidgetCreate, WidgetOut
from app.services import widgets as service

router = APIRouter(prefix="/widgets", tags=["widgets"])

@router.post("", response_model=WidgetOut, status_code=201)
def create(payload: WidgetCreate, db = Depends(get_db)) -> WidgetOut:
    return service.create_widget(db, payload)