pytest FastAPI - InvalidRequestError collecting tests

[wumofei]

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Example Code

# app/main.py
from fastapi import FastAPI
from app.backend.db import init_db

init_db()
app = FastAPI()


# app/backend/db.py
from sqlmodel import Session, SQLModel, create_engine
import app.backend.models

engine = create_engine("sqlite:///dev.db")

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

def get_session():
    with Session(engine) as session:
        yield session

# tests/shared_fixtures.py
from fastapi.testclient import TestClient
import pytest
from sqlmodel import Session, SQLModel, create_engine
from app.backend.db import get_session
from app.main import app

@pytest.fixture
def session():
    engine = create_engine("sqlite://")
    SQLModel.metadata.create_all(engine)
    with Session(engine) as session:
        yield session

@pytest.fixture
def client(session):
    def get_session_override():
        return session
    app.dependency_overrides.clear()
    app.dependency_overrides[get_session] = get_session_override
    with TestClient(app, follow_redirects=False) as test_client:
        yield test_client
    app.dependency_overrides.clear()

Description

• fastapi dev seems to work
• python -m pytest fails during collection, specifically with

sqlalchemy.exc.InvalidRequestError: Table 'mytable' is already defined for this MetaData instance.
Specify 'extend_existing=True' to redefine options and columns on an existing Table object.

Operating System

macOS

Operating System Details

No response

Project Version

0.0.48

Python Version

3.13.6

Additional Context

No response

[Muguett-DBY]

create_all() uses the tables already registered on SQLModel.metadata; it doesn't itself redefine the model. One possible cause is the same model file being loaded under two names, such as app.backend.models and backend.models. Two separate model classes with the same __tablename__ can produce the same error.

I reproduced the duplicate-registration error by executing one model definition under two module names with SQLModel 0.0.48 and SQLAlchemy 2.1.6 on Python 3.12. That doesn't establish which case is happening in your project.

Could you share the full collection traceback, the mytable model definition, and the pytest command and working directory? I would hold off on extend_existing=True until the duplicate registration is understood.