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Fixed the ordering of prefetch lookups so that latter lookups can refer to former lookups.
Thanks Anssi Kääriäinen and Tim Graham for the reviews. Refs #17001 and #22650.
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@ -2,8 +2,8 @@
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The main QuerySet implementation. This provides the public API for the ORM.
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"""
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from collections import deque
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import copy
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import itertools
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import sys
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from django.conf import settings
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@ -1680,6 +1680,9 @@ class Prefetch(object):
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return self.prefetch_to == other.prefetch_to
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return False
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def __hash__(self):
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return hash(self.__class__) ^ hash(self.prefetch_to)
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def normalize_prefetch_lookups(lookups, prefix=None):
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"""
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@ -1713,11 +1716,12 @@ def prefetch_related_objects(result_cache, related_lookups):
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# ensure we don't do duplicate work.
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done_queries = {} # dictionary of things like 'foo__bar': [results]
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auto_lookups = [] # we add to this as we go through.
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auto_lookups = set() # we add to this as we go through.
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followed_descriptors = set() # recursion protection
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all_lookups = itertools.chain(related_lookups, auto_lookups)
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for lookup in all_lookups:
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all_lookups = deque(related_lookups)
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while all_lookups:
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lookup = all_lookups.popleft()
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if lookup.prefetch_to in done_queries:
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if lookup.queryset:
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raise ValueError("'%s' lookup was already seen with a different queryset. "
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@ -1788,7 +1792,9 @@ def prefetch_related_objects(result_cache, related_lookups):
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# the new lookups from relationships we've seen already.
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if not (lookup in auto_lookups and descriptor in followed_descriptors):
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done_queries[prefetch_to] = obj_list
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auto_lookups.extend(normalize_prefetch_lookups(additional_lookups, prefetch_to))
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new_lookups = normalize_prefetch_lookups(additional_lookups, prefetch_to)
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auto_lookups.update(new_lookups)
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all_lookups.extendleft(new_lookups)
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followed_descriptors.add(descriptor)
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else:
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# Either a singly related object that has already been fetched
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@ -1827,7 +1833,6 @@ def get_prefetcher(instance, attr):
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a boolean that is True if the attribute has already been fetched)
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"""
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prefetcher = None
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attr_found = False
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is_fetched = False
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# For singly related objects, we have to avoid getting the attribute
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@ -1835,16 +1840,7 @@ def get_prefetcher(instance, attr):
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# on the class, in order to get the descriptor object.
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rel_obj_descriptor = getattr(instance.__class__, attr, None)
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if rel_obj_descriptor is None:
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try:
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rel_obj = getattr(instance, attr)
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attr_found = True
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# If we are following a lookup path which leads us through a previous
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# fetch from a custom Prefetch then we might end up into a list
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# instead of related qs. This means the objects are already fetched.
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if isinstance(rel_obj, list):
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is_fetched = True
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except AttributeError:
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pass
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attr_found = hasattr(instance, attr)
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else:
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attr_found = True
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if rel_obj_descriptor:
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@ -1889,10 +1885,10 @@ def prefetch_one_level(instances, prefetcher, lookup, level):
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rel_qs, rel_obj_attr, instance_attr, single, cache_name = (
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prefetcher.get_prefetch_queryset(instances, lookup.get_current_queryset(level)))
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# We have to handle the possibility that the default manager itself added
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# prefetch_related lookups to the QuerySet we just got back. We don't want to
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# trigger the prefetch_related functionality by evaluating the query.
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# Rather, we need to merge in the prefetch_related lookups.
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# We have to handle the possibility that the QuerySet we just got back
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# contains some prefetch_related lookups. We don't want to trigger the
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# prefetch_related functionality by evaluating the query. Rather, we need
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# to merge in the prefetch_related lookups.
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additional_lookups = getattr(rel_qs, '_prefetch_related_lookups', [])
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if additional_lookups:
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# Don't need to clone because the manager should have given us a fresh
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@ -195,7 +195,7 @@ class PrefetchRelatedTests(TestCase):
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def test_reverse_one_to_one_then_m2m(self):
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"""
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Test that we can follow a m2m relation after going through
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the select_related reverse of a o2o.
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the select_related reverse of an o2o.
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"""
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qs = Author.objects.prefetch_related('bio__books').select_related('bio')
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@ -559,13 +559,16 @@ class CustomPrefetchTests(TestCase):
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inner_rooms_qs = Room.objects.filter(pk__in=[self.room1_1.pk, self.room1_2.pk])
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houses_qs_prf = House.objects.prefetch_related(
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Prefetch('rooms', queryset=inner_rooms_qs, to_attr='rooms_lst'))
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with self.assertNumQueries(3):
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with self.assertNumQueries(4):
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lst2 = list(Person.objects.prefetch_related(
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Prefetch('houses', queryset=houses_qs_prf.filter(pk=self.house1.pk), to_attr='houses_lst')))
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Prefetch('houses', queryset=houses_qs_prf.filter(pk=self.house1.pk), to_attr='houses_lst'),
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Prefetch('houses_lst__rooms_lst__main_room_of')
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))
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self.assertEqual(len(lst2[0].houses_lst[0].rooms_lst), 2)
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self.assertEqual(lst2[0].houses_lst[0].rooms_lst[0], self.room1_1)
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self.assertEqual(lst2[0].houses_lst[0].rooms_lst[1], self.room1_2)
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self.assertEqual(lst2[0].houses_lst[0].rooms_lst[0].main_room_of, self.house1)
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self.assertEqual(len(lst2[1].houses_lst), 0)
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# Test ReverseSingleRelatedObjectDescriptor.
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