Python 测试：从 Pytest 固定装置播种数据库

Question

I am currently trying to follow a wonderful tutorial around setting up and tearing down databases in a testing environment. Everything works well except for the seed_database() call which throws the following error.

AttributeError: 'function' object has no attribute 'add'

Some questions:

1. Why is db_session even defined when I run seed_database ? It's not being passed in anywhere... My initial guess was that it has something to do with the way Python fixtures work, but it seems a little magical.
2. What changes can I make for db_session to actually be a proper scoped_session?

test_config.py

@pytest.fixture(scope="session")
def connection():
    engine = create_engine(
        "mysql+mysqldb://{}:{}@{}:{}/{}".format(
            os.environ.get('TEST_DB_USER'),
            os.environ.get('TEST_DB_PASSWORD'),
            os.environ.get('TEST_DB_HOST'),
            os.environ.get('TEST_DB_PORT'),
            os.environ.get('TEST_DB_NAME'),
        )
    )
    return engine.connect()


def seed_database():
    users = [
        {
            "id": 1,
            "name": "John Doe",
        },
        # ...
    ]

    for user in users:
        db_user = User(**user)
        db_session.add(db_user)
    db_session.commit()


@pytest.fixture(scope="session")
def setup_database(connection):
    models.Base.metadata.bind = connection
    models.Base.metadata.create_all()
    
    seed_database()

    yield

    models.Base.metadata.drop_all()


@pytest.fixture
def db_session(setup_database, connection):
    transaction = connection.begin()
    yield scoped_session(
        sessionmaker(autocommit=False, autoflush=False, bind=connection)
    )
    transaction.rollback()

test_user.py

from tests.test_config import db_session, setup_database, connection

def test_something(db_session):
    # Some code here...

Answer 1

Why is db_session even defined when I run seed_database?

In Python functions are objects like other. Hence the 'function' object in the error message. db_session is defined in the module and therefore is accessible within seed_database . The only "magic" is that you actually cannot call db_session because Pytest fixtures cannot be called directly.

What changes can I make for db_session to actually be a proper scoped_session?

I think that you might have a "chicken and egg" situation: db_session uses setup_database fixture which calls seed_database which requires db_session to already return the session. You would need to reorganise the code to get out of this.

Without being familiar with the database sessions that you are using it's a bit of a guess work for me but maybe something like this would work:

def seed_database(db_session):
    users = [
        {
            "id": 1,
            "name": "John Doe",
        },
        # ...
    ]

    for user in users:
        db_user = User(**user)
        db_session.add(db_user)

    db_session.commit()

@pytest.fixture
def db_session(setup_database, connection):
    transaction = connection.begin()
    session = scoped_session(
        sessionmaker(autocommit=False, autoflush=False, bind=connection)
    )
    seed_database(db_session=session)
    yield session
    transaction.rollback()

...and you would remove seed_database() call from setup_database .