order_by() has no effect on values()/values_list() in models registered for translation

[mick88]

I have encounteded a bug with a model that has default ordering. I am making a query with order_by() without parameters to avoid ordering and then use values() or values_list() to extract a subset of fields. The end result is an ordered queryset.

It appears that values() restores model's default ordering if called after order_by(), except if queryset is already ordered by cystom ordering (e.g. order_by('name')), in which case order_by is maintained.

Django 3.2.16
Python 3.10
django-modeltranslation 0.18.5

The model:

class Dashboard(models.Model):
    name = models.CharField(max_length=100)
    order = models.PositiveIntegerField(default=1)

    class Meta:
        ordering = 'order',

@register(models.Dashboard)
class DashboardTranslation(TranslationOptions):
    fields = 'name',

Note: it is important that the model defines ordering

To reproduce issue:

# Queryset is ordered by default field as expected ✔
Dashboard.objects.all().values('name').ordered
Out[44]: True

# Queryset is not ordered after adding order_by() as expected ✔
Dashboard.objects.all().order_by().ordered
Out[54]: False

# adding values() call somehow restores default ordering. Expected behaviour is for QS to remain unordered ✖
Dashboard.objects.all().order_by().values('name').ordered
Out[42]: True

# placing order_by() after values() works as expected ✔
Dashboard.objects.all().values('name').order_by().ordered
Out[48]: False

I originally raised the issue in Django bugtracker, but when it wan't reproduced, I debugged it locally and realized that the model uses translations and modeltranslations overrides values() and does not call super().

[mick88]

Added MR #656 that demonstrates the bug

[last-partizan]

Great work reproducing issue.

I currently don't have time to debug this myself, but i have time to review a fix if you can figure it out.

[mick88]

It looks like the culprit is the _post_init() method in queryset. It sets order from model if not set:

    def _post_init(self):
        self._rewrite = True
        self._populate = None
        if self.model and (not self.query.order_by):
            if self.model._meta.ordering:
                # If we have default ordering specified on the model, set it now so that
                # it can be rewritten. Otherwise sql.compiler will grab it directly from _meta
                ordering = []
                for key in self.model._meta.ordering:
                    ordering.append(rewrite_order_lookup_key(self.model, key))
                self.query.add_ordering(*ordering)

[mick88]

Updated my MR with a proposed patch. This passes my test and the other tests in the suite. Please review #656

[last-partizan]

Looks good. Merged, thanks.