Commit 5a9338ae by Diederik van der Boor

Optimize the query in `bulk_lookup_kwargs` for QuerySet args.

When passing a QuerySet to bulk_lookup_kwargs(), the queryset was
undesirably executed to get a list of IDs. This causes an unnecessary
performance loss.

There is no need to loop over a QuerySet to execute a IN (1, 3, 4) query.
Instead, just allow the ORM and database to execute a IN (SELECT id FROM ..) query.
In a real life app with a large set of objects, the difference in performance is noticeable.
parent 36f6dabc
......@@ -2,6 +2,7 @@ import django
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes.generic import GenericForeignKey
from django.db import models, IntegrityError, transaction
from django.db.models.query import QuerySet
from django.template.defaultfilters import slugify as default_slugify
from django.utils.translation import ugettext_lazy as _, ugettext
......@@ -137,6 +138,13 @@ class GenericTaggedItemBase(ItemBase):
@classmethod
def bulk_lookup_kwargs(cls, instances):
if isinstance(instances, QuerySet):
# Can do a real object_id IN (SELECT ..) query.
return {
"object_id__in": instances,
"content_type": ContentType.objects.get_for_model(instances.model),
}
else:
# TODO: instances[0], can we assume there are instances.
return {
"object_id__in": [instance.pk for instance in instances],
......
......@@ -215,6 +215,27 @@ class TaggableManagerTestCase(BaseTaggingTestCase):
[kitty.pk, cat.pk]
)
def test_lookup_bulk(self):
apple = self.food_model.objects.create(name="apple")
pear = self.food_model.objects.create(name="pear")
apple.tags.add('fruit', 'green')
pear.tags.add('fruit', 'yummie')
def lookup_qs():
# New fix: directly allow WHERE object_id IN (SELECT id FROM ..)
objects = self.food_model.objects.all()
lookup = self.taggeditem_model.bulk_lookup_kwargs(objects)
list(self.taggeditem_model.objects.filter(**lookup))
def lookup_list():
# Simulate old situation: iterate over a list.
objects = list(self.food_model.objects.all())
lookup = self.taggeditem_model.bulk_lookup_kwargs(objects)
list(self.taggeditem_model.objects.filter(**lookup))
self.assert_num_queries(1, lookup_qs)
self.assert_num_queries(2, lookup_list)
def test_exclude(self):
apple = self.food_model.objects.create(name="apple")
apple.tags.add("red", "green", "delicious")
......
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