First, let me thank Malcolm for promptly fixing #10710. Unfortunately
#10733 is still barring the use of only() and select_related()
properly.
Given the models and admin defined above and the requirements that
* admin changelist view should perform only a single query,
* that should pull in only the fields that are actually used in
list_display,
the following should ideally work after #10733 is fixed:
def queryset(self, request):
qs = super(CAdmin, self).queryset(request)
return qs.only('name', 'is_published', 'a', 'b',
'a__name', 'b__name').select_related()
(actually, qs.only('name', 'is_published', 'a__name',
'b__name').select_related() would suffice.)
---
However, there's another bump on the Path to The One True Admin
Changelist Query.
If any of the related fields 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 (as Karen kindly
pointed out in #10722).
Forcing it explicitly as follows
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().
To get the desired behviour, 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.
The patch is backwards-compatible, quite simple and the result is a
single query as expected:
--- django/contrib/admin/views/main.py (revision 10405)
+++ django/contrib/admin/views/main.py (working copy)
@@ -200,6 +200,8 @@
# with a relationship.
if self.list_select_related:
qs = qs.select_related()
+ elif self.list_select_related is None:
+ pass
else:
for field_name in self.list_display:
try:
(validation changes omitted for clarity).
I've submitted the proposal in #10742 and am willing to drive it
further if it is accepted.
---
Finally, after #10733 and #10742 are fixed, the admin and The One True
Admin Changelist Query that satisfies the requirements is 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.only('name', 'is_published', # 'a', 'b' ?
'a__name', 'b__name').select_related('a', 'b')
Links:
#10733 -- http://code.djangoproject.com/ticket/10733
#10742 -- http://code.djangoproject.com/ticket/10742
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Django developers" group.
To post to this group, send email to django-developers@googlegroups.com
To unsubscribe from this group, send email to
django-developers+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/django-developers?hl=en
-~----------~----~----~----~------~----~------~--~---
