Only make a connection to the DB if necessary

[mjvankampen]

When updating to Django 4 I noticed that suddenly our CI failed as there was no valid database while linting migrations. This change will only connect to a DB when it is necessary (i.e. check only applied or unapplied migrations). That way you don't have to do trickery in your settings file when you run the linter without a DB.

[mjvankampen]

Ah sorry not related to Django4 but still I think this PR is valid.

[David-Wobrock]

Hey @mjvankampen ! Thanks for contributing and taking interest in the project 🙇

I'm not sure I get the rationale behind this change 🤔
We still require a DB connection even when we don't specify only applied or unapplied migrations. The MigrationLoader object is still required to load and lint migrations.
I'm not sure it can work with this new condition.

Do you have more context/information about your case? :)

[mjvankampen]

Sorry I’m somewhat new to databases and Django (coming from an embedded environment). While setting up CI/CD I noticed that to lint migrations you need to connect to the database. On a higher level I don’t really understand that as you don’t need to know the current state of the database as that is captured in your migrations already. Except if you only want to lint unapplied migrations for example.

From your reply the MigrationLoader is needed to lint the migrations and the MigrationLoader needs a connection to a database (the state of the db does not matter?) which is I guess hard to get around.

Ps. Love the project and its helped me capture some bad migrations already!

Please let me know if I understand correctly, then I’ve learned something and will work around it (like spin up a DB for linting).