Why Alembic does not detect models without importing them?

[albertalexandrov]

Hi all!

Imagine there is a base class:

models/base.py:

from typing import Self

from sqlalchemy import MetaData
from sqlalchemy.orm import DeclarativeBase

metadata = MetaData()


class Model(DeclarativeBase):
    metadata = metadata

    def update(self, **values) -> Self:
        for key, value in values.items():
            setattr(self, key, value)
        return self

and some subclass:

models/users.py:

from models.base import Model
from sqlalchemy.orm import Mapped, mapped_column


class User(Model):
    __tablename__ = "users"

    id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)

I'd like to use metadata instance in env.py but model User is not being detected by Alembic:

env.py

import asyncio
from logging.config import fileConfig

from somewhere import engine

from models.base import metadata  <=== import

from sqlalchemy import pool
from sqlalchemy.engine import Connection
from sqlalchemy.ext.asyncio import async_engine_from_config

from alembic import context

config = context.config

if config.config_file_name is not None:
    fileConfig(config.config_file_name)

config.set_main_option("sqlalchemy.url", engine.sync_engine.url.render_as_string(hide_password=False))


def do_run_migrations(connection: Connection) -> None:
    context.configure(connection=connection, target_metadata=metadata)
    with context.begin_transaction():
        context.run_migrations()


async def run_async_migrations() -> None:
    connectable = async_engine_from_config(
        config.get_section(config.config_ini_section, {}),
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )
    async with connectable.connect() as connection:
        await connection.run_sync(do_run_migrations)
    await connectable.dispose()


def run_migrations_online() -> None:
    asyncio.run(run_async_migrations())


run_migrations_online()

but if to import some of subclasses of Model then it works:

from models.users import User
from models.base import metadata  <=== import

Why it work in this way? How to make Alembic detect models without importing User?

[CaselIT]

Hi,

That's just how python works, it evaluates modules lazily, the first time you access them.
An usual solution to ensure that all models are import is to make use of a module file that imports all models in a single place, so you can import it and you are fine. __init__ is usually used for this.

In you case you could add inside the models package and __init__.py file that has something like

from .base import metadata

from .users import User
...

so in alembic env you can then just add from models import metadata

[albertalexandrov]

Thanks) I did like this