python 52 lines · 8 steps

Building a signup endpoint in FastAPI

A user-registration route that validates input, checks for duplicates, persists to the database, and sends a welcome email in the background.

Explained by highlit
FastAPI Intermediate dependency-injection request-validation background-tasks orm rest-api
1from fastapi import APIRouter, BackgroundTasks, Depends, HTTPException, status
2from pydantic import BaseModel, EmailStr
3from sqlalchemy.orm import Session
4 
5from .database import get_db
6from .models import User
7from .services.mailer import send_email
8 
9router = APIRouter(prefix="/users", tags=["users"])
10 
11 
12class SignupRequest(BaseModel):
13 email: EmailStr
14 full_name: str
15 
16 
17class SignupResponse(BaseModel):
18 id: int
19 email: EmailStr
20 
21 class Config:
22 from_attributes = True
23 
24 
25def send_welcome_email(email: str, full_name: str) -> None:
26 send_email(
27 to=email,
28 subject="Welcome aboard!",
29 template="welcome",
30 context={"name": full_name},
31 )
32 
33 
34@router.post("", response_model=SignupResponse, status_code=status.HTTP_201_CREATED)
35def signup(
36 payload: SignupRequest,
37 background_tasks: BackgroundTasks,
38 db: Session = Depends(get_db),
39) -> User:
40 if db.query(User).filter(User.email == payload.email).first():
41 raise HTTPException(
42 status_code=status.HTTP_409_CONFLICT,
43 detail="A user with this email already exists.",
44 )
45 
46 user = User(email=payload.email, full_name=payload.full_name)
47 db.add(user)
48 db.commit()
49 db.refresh(user)
50 
51 background_tasks.add_task(send_welcome_email, user.email, user.full_name)
52 return user
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Pydantic models validate incoming JSON and shape outgoing responses, keeping the endpoint body free of manual parsing.
  2. 2Depends lets FastAPI inject a per-request database session so the handler never manages its own connection lifecycle.
  3. 3BackgroundTasks defers slow work like email until after the response is sent, keeping the request fast.

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