Simplify migrations

[yajo]

The current migrations workflow is quite difficult to maintain.

The goal was to give full flexibility, but after some usage, it seems to make things more difficult.

Instead of having a migrations definition such as this:

_migrations:
  - version: v1.0.0
    before:
      - &mig
        - "[[ _copier_conf.src_path / 'migrations.py' ]]"
        - "[[ _copier_conf|tojson ]]"
    after:
      - *mig
  - version: v2
    before: [*mig]
    after:
      - *mig
      - "rm delete-in-migration-$VERSION_CURRENT.txt"

We should be having something like this:

_migrations:
  working_directory: "[[ _copier_conf.src_path ]]" # default value
  command: [poetry, run, migrations.py]

Then, all data needed for migrations will be passed as env variables, which that script can load and use to handle all of them comfortably.

At the end of the day, that code is easier to maintain in a migrations script, and this way we avoid the need to repeat the same definition once and again for each version (as seen in the 1st example using *mig).

[pawamoy]

Just curious: what kind of commands do you need to run for every new version, and also before and after each update? Or is you script dealing with all these states, and most of the time not executing anything?

[yajo]

Or is you script dealing with all these states, and most of the time not executing anything?

Yes, that's what will happen most of the time

[pawamoy]

OK thanks. Indeed it might be easier to maintain a separate shell/Python script than cluttering copier.yml over time and new versions (even though technically one can get rid of old migrations in copier.yml at each new release, since the old migrations are still contained in the old versions themselves, thanks to git).

[yajo]

even though technically one can get rid of old migrations in copier.yml at each new release, since the old migrations are still contained in the old versions themselves, thanks to git

Beware with that... Migrations are loaded on the latest tag always, and all of them that apply are run sequentially, but Copier won't checkout each of them individually. Otherwise, you could never fix a bug in your migration script.

[pawamoy]

Oh yes you're right, my bad. Then I'm definitely in favor of what you propose here.

[AdrianFreundQC]

I'll take a look at implementing this.