ModelAdmin.list_select_related needs three-valued logic to support custom select_related() calls

[mrts]

If any of the related fields in a model is nullable, e.g.

class C(Base):
    a = models.ForeignKey(A, blank=True, null=True)
    b = models.ForeignKey(B)
    is_published = models.BooleanField()

, select_related() does not pull them in by default (see ​http://docs.djangoproject.com/en/dev/ref/models/querysets/#select-related).

Forcing it explicitly as follows

class CAdmin(admin.ModelAdmin):
    list_display = ('name', 'a', 'b', 'is_published')
    list_select_related = None

    def queryset(self, request):
        qs = super(CAdmin, self).queryset(request)
        return qs.select_related('a', 'b')

has no effect, as ChangeList.get_query_set() blindly overrides it with a plain select_related() (see [source:django/trunk/django/contrib/admin/views/main.py@10407#L201]).

To get the desired behviour of pulling in the nullable relations in a single query, three-valued logic is required for ModelAdmin.list_select_related:

• True -- always call select_related(),
• False (the default) -- call select_related() if any of the fields in list_display is a foreign key,
• None (added) -- leave the queryset alone.

Patch attached.

See also #10722 and ​http://groups.google.com/group/django-developers/browse_thread/thread/e1762a77979f7cbe .

[mrts]

(I'll write proper tests and docs if this is accepted.)

[Jacob]

Duplicate of #10348

[Jacob]

Milestone 1.1 deleted