Dabase creation backend should use base_manager to serialize database

[Eugene K]

models.py

class Service(Model):
    objects = CustomManagerThatFillterOutSomeRecords()

class CustomManagerThatFillterOutSomeRecords(Manager):
    def get_queryset(self):
        return super().get_queryset().exclude(pk=1)

tests.py

class TestService(TransactionTestCase):
    serialized_rollback = True

    def test_something(self):
        pass

Assume we have a migration that creates few records of Service.

from django.core.management import call_command
from django.db import migrations


def load_fixtures(*_, **__):
    call_command('loaddata', 'services.json')


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

    operations = [
        migrations.RunPython(
            load_fixtures,
            migrations.RunPython.noop,
        )
    ]

Then TestService will fail as serialize_db_to_string by default use _default_manager that is CustomManagerThatFillterOutSomeRecords.

Here is proposed fix: ​https://github.com/django/django/pull/13150

[Simon Charette]

That makes sense.

You'll need to add regression tests to your PR in [django/db/backends/base/creation.py ​https://github.com/django/django/blob/4d9cd89acbb944e10b9000092069ba8e3a855957/django/db/backends/base/creation.py] by defining a default manager that exclude rows django/db/backends/models.py, creating one such row, and ensure it's part of the string returned by serialize_db_to_string.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 50c3ac6:

Fixed #31762 -- Made reloading the database for tests use the base manager.

Co-authored-by: Eugene Kulak <kulak.eugene@…>