Documented testing approach does not work for SQLite in-memory instances

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Example Code

# ----------------------------------------------------------------
# app.py

from __future__ import annotations

from fastapi import Depends, FastAPI
from sqlalchemy import Column, Integer, create_engine
from sqlalchemy.orm import Session, declarative_base, sessionmaker  # type: ignore

Base = declarative_base()


class DbExample(Base):  # type: ignore
    __tablename__ = "app_examples"

    example_id = Column(Integer, primary_key=True)


def create_db(url: str):
    engine = create_engine(
        url,
        connect_args={"check_same_thread": False},
        native_datetime=True,
    )
    SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
    Base.metadata.create_all(bind=engine)

    return SessionLocal


SessionLocal = create_db("sqlite:///./real.db")
app = FastAPI()


def get_db():
    db = SessionLocal()

    try:
        yield db
    finally:
        db.close()


@app.get("/")
def summary(*, db: Session = Depends(get_db)):
    res = db.execute("SELECT COUNT(*) FROM app_examples").scalars()

    return {"result": next(res)}

# ----------------------------------------------------------------
# test_app.py

from __future__ import annotations

from fastapi.testclient import TestClient

from app import app, create_db, get_db

TEST_DB_URL = "sqlite://"


def test_root_with_context_manager() -> None:
    from contextlib import contextmanager

    @contextmanager
    def _session():
        TestingSessionLocal = create_db(TEST_DB_URL)
        saved_get_db = get_db in app.dependency_overrides
        old_get_db = app.dependency_overrides.get(get_db)

        def override_get_db():
            try:
                db = TestingSessionLocal()
                yield db
            finally:
                db.close()

        app.dependency_overrides[get_db] = override_get_db

        try:
            yield
        finally:
            if saved_get_db:
                app.dependency_overrides[get_db] = old_get_db

    with _session():
        client = TestClient(app)
        client.get("/")


def test_root_with_patch() -> None:
    from unittest.mock import patch

    TestingSessionLocal = create_db(TEST_DB_URL)

    with patch("app.SessionLocal", TestingSessionLocal):
        client = TestClient(app)
        client.get("/")


def test_root_by_hand() -> None:
    # Trying to follow <https://fastapi.tiangolo.com/advanced/testing-database/>
    from sqlalchemy import create_engine
    from sqlalchemy.orm import sessionmaker

    from app import Base

    engine = create_engine(
        TEST_DB_URL,
        connect_args={"check_same_thread": False},
        native_datetime=True,
    )
    TestingSessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
    Base.metadata.create_all(bind=engine)

    def override_get_db():
        try:
            db = TestingSessionLocal()
            yield db
        finally:
            db.close()

    app.dependency_overrides[get_db] = override_get_db
    client = TestClient(app)
    client.get("/")

Description

The above is modeled after these instructions, but those do not appear to work for SQLite’s in-memory databases. Running the following tests results in three errors similar to:

E       sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) no such table: app_examples
E       [SQL: SELECT COUNT(*) FROM app_examples]
E       (Background on this error at: https://sqlalche.me/e/14/e3q8)

Changing TEST_DB_URL to, e.g., sqlite:///./test.db allows those tests to pass.

Operating System

Linux, macOS

Operating System Details

No response

FastAPI Version

0.68.1

Python Version

Python 3.9.6

Additional Context

No response

[jnnnnn]

I got this to work following #1223 with:

from sqlalchemy.pool import StaticPool
engine = create_engine("sqlite://", connect_args={"check_same_thread": False}, poolclass=StaticPool)

[Dentosal]

Using this solution works for me:

from sqlalchemy.pool import StaticPool
...
engine = create_engine(
    "sqlite:///:memory:", connect_args={"check_same_thread": False},
    poolclass=StaticPool
)