python 48 lines · 8 steps

How a Flask blueprint validates and creates users

A Flask blueprint pairs a Marshmallow schema with a POST route to validate input, reject duplicates, and persist a new user.

Explained by highlit
Flask Intermediate validation rest-api schema orm input-sanitization
1from flask import Blueprint, request, jsonify
2from marshmallow import Schema, fields, validate, ValidationError, EXCLUDE
3 
4from .models import db, User
5from .services import send_welcome_email
6 
7bp = Blueprint("users", __name__, url_prefix="/api/users")
8 
9 
10class CreateUserSchema(Schema):
11 class Meta:
12 unknown = EXCLUDE
13 
14 email = fields.Email(required=True)
15 username = fields.Str(
16 required=True,
17 validate=validate.Length(min=3, max=32),
18 )
19 password = fields.Str(
20 required=True,
21 load_only=True,
22 validate=validate.Length(min=8),
23 )
24 age = fields.Int(validate=validate.Range(min=13, max=120))
25 
26 
27create_user_schema = CreateUserSchema()
28 
29 
30@bp.post("")
31def create_user():
32 try:
33 data = create_user_schema.load(request.get_json(force=True))
34 except ValidationError as err:
35 return jsonify(errors=err.messages), 422
36 
37 if User.query.filter_by(email=data["email"]).first():
38 return jsonify(errors={"email": ["already registered"]}), 409
39 
40 user = User(email=data["email"], username=data["username"], age=data.get("age"))
41 user.set_password(data["password"])
42 
43 db.session.add(user)
44 db.session.commit()
45 
46 send_welcome_email.delay(user.id)
47 
48 return jsonify(id=user.id, email=user.email, username=user.username), 201
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Validating request bodies with a schema keeps parsing, type coercion, and error handling out of your route logic.
  2. 2Checking for existing records before insert lets you return a meaningful conflict status instead of a database error.
  3. 3Offloading side effects like emails to a background task keeps the request path fast and responsive.

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