Alembic, SQLAlchemy and multiple "apps" inside a project

Question

Coming to SQLAlchemy from the world of Django, I would like to have a project split into several apps, where models and views are bunched together according to their purpose.

For example, I am writing a planner app, I would like to have Users and Plans to live in separate apps inside my project. I want to make sure that if I have to split this project into smaller ones, I would have the least amount of work to do possible.

I also would like to be able to generate and run migrations with one command correspondingly, so that I don't have to reconfigure my CI builds every time I add a model or an "app".

So far what I could come up with in this respect is

project structure:

my_planner
  +- users
  |  +- migrations
  |  |  +- versions
  |  |  |  +- 0000_initial.py
  |  |  +- __init__.py
  |  |  +- env.py
  |  |  +- script.py.mako
  |  +- __init__.py
  |  +- models.py
  +- plans (same structure as users)

alembic.ini:

[alembic]
script_location = alembic/migrations # this doesn't seem to matter
version_locations = users/migrations/versions plans/migrations/options

[users]
script_location = users/migrations

[plans]
script_location = plans/migrations

And then I had to place env.py files into my migrations folders and import the models I want to be included into automatic migrations.

However, when I generate my automatic migrations, I have to specify the exact "apps" for which I generate them and specify a branch.

PYTHONPATH=. alembic --name users revision -m 'initial'  --rev-id='0000' --branch-label users --autogenerate

And when I apply the migrations, I have to apply them separately for each of the branches.

Is there a way to do these things in one command correspondingly without writing my own custom scripts? Or is there another approach to managing migrations?

As I am still thinking about this, a possible solution would be to keep separate "alembic root folders" in each of the app folders. And then have a separate build script to find all such folders and run commands against them. Still, doesn't seem like an elegant solution. (Just tried that, it did the same as I did manually copying the alembic folders into neighbouring projects). — Ibolit, Feb 28 '20 at 09:05

score 1 · Accepted Answer · answered Jul 06 '20 at 08:00

Unfortunately, I've not found an out of the box way to do this. I wrote about the approach we went with here.

The gist of it is;

Create common migration functionality
Add a migrations directory with app specific information to each app(schema, metadata)
Add your relevant app sections to the alembic.ini file, referring to each directory
Use branches starting from the base to track each app's migrations separately

Alembic, SQLAlchemy and multiple "apps" inside a project

1 Answers1