FastAPI POST not validating missing fields with SQLModel like it does with BaseModel subclass

[andrewnathanco]

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Example Code

from sqlmodel import Field, SQLModel, create_engine
from datetime import datetime
from fastapi import FastAPI
from sqlmodel import Session
from pydantic import BaseModel
import uuid

sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"

engine = create_engine(sqlite_url, echo=True)

def create_db_and_tables():
    SQLModel.metadata.create_all(engine)


class HeroBase(BaseModel):
    name: str
    power: str
    weakness: str

class Hero(SQLModel, table=True):
    id: str = Field(default=None, primary_key=True)
    name: str
    power: str
    weakness: str

api = FastAPI()

@api.on_event("startup")
async def startup_event():
    create_db_and_tables()

@api.post("/heroes")
async def create_hero(hero: Hero):
    with Session(engine) as session:
        hero.id = str(uuid.uuid4())
        session.add(hero)
        session.commit()
        session.refresh(hero)
        return hero

Description

based on these docs: https://sqlmodel.tiangolo.com/tutorial/fastapi/simple-hero-api/

if you run the above code and try to post the following

{
    "name": "hero"
}

you should expect to see

{
    "detail": [
        {
            "type": "missing",
            "loc": [
                "body",
                "power"
            ],
            "msg": "Field required",
            "input": {
                "name": "hero"
            }
        },
        {
            "type": "missing",
            "loc": [
                "body",
                "weakness"
            ],
            "msg": "Field required",
            "input": {
                "name": "hero"
            }
        }
    ]
}

in fact, when you switch the body python type for that API from Hero to HeroBase which uses BaseModel from pydantic you do.

but if you run it with Hero as is outlined in the docs, you get a 500 internal server error and a non null constraint.

sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) NOT NULL constraint failed: hero.power
[SQL: INSERT INTO hero (id, name, power, weakness) VALUES (?, ?, ?, ?)]
[parameters: ('c40b0cdf-2a3d-402d-90c5-321c01740190', 'hero', None, None)]
(Background on this error at: https://sqlalche.me/e/20/gkpj)

which means fastapis built in validation is not working allowing the model to be read even with missing fields causing the database error. which directly contradicts this line from the docs

Because FastAPI is based on Pydantic, it will use the same model (the Pydantic part) to do automatic data validation and conversion from the JSON request to an object that is an actual instance of the Hero class.

Operating System

macOS

Operating System Details

No response

SQLModel Version

0.0.27

Python Version

Python 3.13.3

Additional Context

No response

[YuriiMotov]

You shouldn't use table-model (with table=True) for validation. Create base class with common fields (excluding relationships) and inherit input validation model and table-model from that base class.

See: https://sqlmodel.tiangolo.com/tutorial/fastapi/multiple-models/#multiple-models-with-inheritance

[andrewnathanco]

thank you, this section of docs is a bit misleading, https://sqlmodel.tiangolo.com/tutorial/fastapi/simple-hero-api/#create-heroes-path-operation as it implies that it will work out of the box, but your answer should fix it