post-migrate handlers fail when DATABASES['default'] = {}

[Thomas Recouvreux]

On Django 1.7.4 the management command migrate --database=xxx fails when DATABASES['default'] = {} with django.core.exceptions.ImproperlyConfigured: settings.DATABASES is improperly configured. Please supply the ENGINE value. Check settings documentation for more details..
On Django 1.7.3 it works fine.

To reproduct the problem:

1. Create a new project
2. Edit the settings.py this way:

DATABASES = {
    'default': {},
    'mysite': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db_mysite.sqlite3'),
    }
}

3. Run python manage.py migrate --database=mysite

Problem:

It seems Django tries to access the default connection. I found django.db.migrations.loader.is_latest_migration_applied uses the default connection.

I am attaching an output log of the command.
Here is a sample project to reproduce the behaviour: ​https://github.com/trecouvr/test_dj_migrate_174.

[Marten Kenbeek]

Seems easy enough, only 3 occurrences in the whole code-base.

[Marten Kenbeek]

Patch: ​https://github.com/knbk/django/compare/ticket_24298

I'm not too sure on the tests, I'd like some feedback on that before I create a pull request.

[Markus Holtermann]

I'm about to revert the patches for #24075.

[Markus Holtermann]

Fixed in bd3d796ecd9a66832ad26024df65caeb63b60a5d and 2832a9b028c267997b2fd3dd0989670d57cdd08f.

[awol]

I think there is an additional failure scenario in the Sites application. I haven't had the chance to track down the source of the defect in Sites, in the event that I do, should I reopen this ticket or submit a new ticket?

[Thomas Recouvreux]

Thank you for the quick updates. Following the report of awol I updated my test project and added a log file. I found the problem might come from the django.contrib.sites.management.create_default_site function which calls Site.objects.exists without propagating the using parameter. I dont know either if I should create a new ticket or not.

[Markus Holtermann]

Although it's a similar issue (missing use of using), it is still due to another bug. It should be Site.objects.using(using).exists() in line 20.

Please open a separate issue for that.