1. APIRouter and resource-oriented URLs
Start with the contract: make inputs, outputs and failure behavior explicit before adding infrastructure. This keeps the feature easy to reason about and gives tests a stable boundary.
2. Request, response and patch models
Apply the pattern through a small vertical slice. Keep framework wiring at the edge and business decisions in focused functions or services that can be tested without starting the whole application.
from fastapi import APIRouter, HTTPException, status
from pydantic import BaseModel, Field
router = APIRouter(prefix="/tasks", tags=["tasks"])
class TaskCreate(BaseModel):
title: str = Field(min_length=1, max_length=120)
@router.post("", status_code=status.HTTP_201_CREATED)
def create_task(body: TaskCreate):
return {"id": 1, **body.model_dump()}3. Validation and centralized errors
Treat failure paths as part of the design. Add bounded resource usage, meaningful errors and a verification step so the behavior remains dependable under real production conditions.
4. Hands-on Exercise
Build the feature
Design CRUD endpoints for tasks, including separate create, update and response schemas and consistent 404 responses.
Definition of done
- The happy path works through the real HTTP boundary.
- At least one failure path is handled and tested.
- Configuration and secrets stay outside source code.
- The README explains how to run and verify the result.
5. Knowledge Check
Why use a separate response model instead of returning the database object?
Show answer
It creates a stable public contract and prevents internal or sensitive fields from leaking.