Reversing CreateExtension throws error on non-postgresql database

[Jori Niemi]

When run on sqlite, a migration using postgres CreateExtension will skip creating the extension. Trying to reverse the migration throws an error:

django.db.utils.OperationalError: no such table: pg_extension

I assume this is because CreateExtension.database_forwards checks schema_editor.connection.vendor != "postgresql" but CreateExtension.database_backwards does not.

Minimal migration example:

from django.db import migrations
from django.contrib.postgres.operations import CreateExtension

class Migration(migrations.Migration):
    dependencies = []

    operations = [
        CreateExtension("pg_trgm")
    ]

[Lakshya Prasad]

I can reproduce this issue locally. Reversing CreateExtension on a
non-PostgreSQL database raises an error. The operation should likely
be skipped when the connection vendor is not PostgreSQL.

I’d like to work on a fix if the ticket is accepted.

[Jacob Walls]

Ok, let's have this. Interestingly, this graceful skip in the forward direction was only added for Django's own test suite in 36e90d1f45a13f53ce25fdc2d9c04433b835c9af.

[Lakshya Prasad]

Hi Varun, are you currently working on this ticket? If not, I’d be happy to contribute a fix.

[Varun Kasyap Pentamaraju]

Replying to Lakshya Prasad:

Hi Varun, are you currently working on this ticket? If not, I’d be happy to contribute a fix.

Hi Lakshya,
I have a patch and will be submitting soon. Thanks

[Varun Kasyap Pentamaraju]

​https://github.com/django/django/pull/20964

[Jacob Walls <jacobtylerwalls@…>]

In b38cddf8:

Fixed #36985 -- Skipped CreateExtension backwards operation on non-PostgreSQL databases.