#24873: Error while using Prefech on more than two levels
-------------------------------------+-------------------------------------
Reporter: Gagaro | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: Prefetch | Triage Stage: Accepted
prefetch_related |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Description changed by Gagaro:
Old description:
> Given the following models:
>
> {{{
> class A(models.Model):
> pass
>
> class B(models.Model):
> a = models.ForeignKey(A, related_name='b')
>
> class C(models.Model):
> b = models.ForeignKey(B, related_name='c')
>
> class D(models.Model):
> c = models.ForeignKey(C, related_name='d')
> }}}
>
> And the following tests:
>
> {{{
> class PrefetchTest(TestCase):
> def setUp(self):
> a = A.objects.create()
> b = B.objects.create(a=a)
> c = C.objects.create(b=b)
> D.objects.create(c=c)
>
> def test_with_prefetch(self):
> c = C.objects.prefetch_related(Prefetch('d'))
> b = B.objects.prefetch_related(Prefetch('c', queryset=c))
> a = A.objects.prefetch_related(Prefetch('b', queryset=b))
> list(a)
>
> def test_without_prefetch(self):
> c = C.objects.prefetch_related('d')
> b = B.objects.prefetch_related(Prefetch('c', queryset=c))
> a = A.objects.prefetch_related(Prefetch('b', queryset=b))
> list(a)
> }}}
>
> The first test will fail while the second will succeed. The backtrace
> with Django 1.8 is:
>
> {{{
> Traceback (most recent call last):
> File
> "/home/gagaro/django/modules/test/django_test/models_test/tests.py", line
> 19, in test_with_prefetch
> list(a)
> File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
> packages/django/db/models/query.py", line 162, in __iter__
> self._fetch_all()
> File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
> packages/django/db/models/query.py", line 967, in _fetch_all
> self._prefetch_related_objects()
> File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
> packages/django/db/models/query.py", line 591, in
> _prefetch_related_objects
> prefetch_related_objects(self._result_cache,
> self._prefetch_related_lookups)
> File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
> packages/django/db/models/query.py", line 1516, in
> prefetch_related_objects
> obj_list, additional_lookups = prefetch_one_level(obj_list,
> prefetcher, lookup, level)
> File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
> packages/django/db/models/query.py", line 1615, in prefetch_one_level
> prefetcher.get_prefetch_queryset(instances,
> lookup.get_current_queryset(level)))
> File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
> packages/django/db/models/fields/related.py", line 729, in
> get_prefetch_queryset
> for rel_obj in queryset:
> File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
> packages/django/db/models/query.py", line 162, in __iter__
> self._fetch_all()
> File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
> packages/django/db/models/query.py", line 967, in _fetch_all
> self._prefetch_related_objects()
> File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
> packages/django/db/models/query.py", line 591, in
> _prefetch_related_objects
> prefetch_related_objects(self._result_cache,
> self._prefetch_related_lookups)
> File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
> packages/django/db/models/query.py", line 1505, in
> prefetch_related_objects
> (through_attr, first_obj.__class__.__name__,
> lookup.prefetch_through))
> AttributeError: Cannot find 'c' on C object, 'c__d' is an invalid
> parameter to prefetch_related()
> }}}
>
> I tested with Django 1.7, 1.8, 1.8.2 and master (commit
> 24718b7dccd64dfa118fe8136e7b175babec679b).
New description:
Given the following models:
{{{
# Foreign Keys
class A(models.Model):
pass
class B(models.Model):
a = models.ForeignKey(A, related_name='b')
class C(models.Model):
b = models.ForeignKey(B, related_name='c')
class D(models.Model):
c = models.ForeignKey(C, related_name='d')
#ManyToMany Fields
class E(models.Model):
pass
class F(models.Model):
e = models.ManyToManyField(E, related_name='f')
class G(models.Model):
f = models.ManyToManyField(F, related_name='g')
class H(models.Model):
g = models.ManyToManyField(G, related_name='h')
}}}
And the following tests:
{{{
class PrefetchForeignKeyTest(TestCase):
def setUp(self):
a = A.objects.create()
b = B.objects.create(a=a)
c = C.objects.create(b=b)
D.objects.create(c=c)
def test_with_prefetch(self):
c = C.objects.prefetch_related(Prefetch('d'))
b = B.objects.prefetch_related(Prefetch('c', queryset=c))
a = A.objects.prefetch_related(Prefetch('b', queryset=b))
list(a)
a.first().b.first().c.first().d.first()
def test_without_prefetch(self):
c = C.objects.prefetch_related('d')
b = B.objects.prefetch_related(Prefetch('c', queryset=c))
a = A.objects.prefetch_related(Prefetch('b', queryset=b))
list(a)
a.first().b.first().c.first().d.first()
class PrefetchManyTest(TestCase):
def setUp(self):
e = E.objects.create()
f = F.objects.create()
g = G.objects.create()
h = H.objects.create()
f.e.add(e)
g.f.add(f)
h.g.add(g)
def test_with_prefetch(self):
g = G.objects.prefetch_related(Prefetch('h'))
f = F.objects.prefetch_related(Prefetch('g', queryset=g))
e = E.objects.prefetch_related(Prefetch('f', queryset=f))
list(e)
e.first().f.first().g.first().h.first()
def test_without_prefetch(self):
g = G.objects.prefetch_related('h')
f = F.objects.prefetch_related(Prefetch('g', queryset=g))
e = E.objects.prefetch_related(Prefetch('f', queryset=f))
list(e)
e.first().f.first().g.first().h.first()
}}}
The tests will fail. The backtrace with master is:
{{{
======================================================================
ERROR: test_with_prefetch (models_test.tests.PrefetchManyTest)
----------------------------------------------------------------------
Traceback (most recent call last):
File
"/home/gagaro/django/modules/test/django_test/models_test/tests.py", line
49, in test_with_prefetch
e.first().f.first().g.first().h.first()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 543, in first
objects = list((self if self.ordered else self.order_by('pk'))[:1])
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 258, in __iter__
self._fetch_all()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1065, in _fetch_all
self._prefetch_related_objects()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 649, in
_prefetch_related_objects
prefetch_related_objects(self._result_cache,
self._prefetch_related_lookups)
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1426, in
prefetch_related_objects
(through_attr, first_obj.__class__.__name__, lookup.prefetch_through))
AttributeError: Cannot find 'f' on F object, 'f__f__g' is an invalid
parameter to prefetch_related()
======================================================================
ERROR: test_without_prefetch (models_test.tests.PrefetchManyTest)
----------------------------------------------------------------------
Traceback (most recent call last):
File
"/home/gagaro/django/modules/test/django_test/models_test/tests.py", line
56, in test_without_prefetch
e.first().f.first().g.first().h.first()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 543, in first
objects = list((self if self.ordered else self.order_by('pk'))[:1])
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 258, in __iter__
self._fetch_all()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1065, in _fetch_all
self._prefetch_related_objects()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 649, in
_prefetch_related_objects
prefetch_related_objects(self._result_cache,
self._prefetch_related_lookups)
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1426, in
prefetch_related_objects
(through_attr, first_obj.__class__.__name__, lookup.prefetch_through))
AttributeError: Cannot find 'f' on F object, 'f__f__g' is an invalid
parameter to prefetch_related()
======================================================================
ERROR: test_with_prefetch (models_test.tests.PrefetchForeignKeyTest)
----------------------------------------------------------------------
Traceback (most recent call last):
File
"/home/gagaro/django/modules/test/django_test/models_test/tests.py", line
23, in test_with_prefetch
list(a)
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 258, in __iter__
self._fetch_all()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1065, in _fetch_all
self._prefetch_related_objects()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 649, in
_prefetch_related_objects
prefetch_related_objects(self._result_cache,
self._prefetch_related_lookups)
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1437, in
prefetch_related_objects
obj_list, additional_lookups = prefetch_one_level(obj_list,
prefetcher, lookup, level)
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1536, in prefetch_one_level
prefetcher.get_prefetch_queryset(instances,
lookup.get_current_queryset(level)))
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/fields/related.py", line 753, in
get_prefetch_queryset
for rel_obj in queryset:
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 258, in __iter__
self._fetch_all()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1065, in _fetch_all
self._prefetch_related_objects()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 649, in
_prefetch_related_objects
prefetch_related_objects(self._result_cache,
self._prefetch_related_lookups)
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1426, in
prefetch_related_objects
(through_attr, first_obj.__class__.__name__, lookup.prefetch_through))
AttributeError: Cannot find 'c' on C object, 'c__d' is an invalid
parameter to prefetch_related()
======================================================================
ERROR: test_without_prefetch (models_test.tests.PrefetchForeignKeyTest)
----------------------------------------------------------------------
Traceback (most recent call last):
File
"/home/gagaro/django/modules/test/django_test/models_test/tests.py", line
31, in test_without_prefetch
a.first().b.first().c.first().d.first()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 543, in first
objects = list((self if self.ordered else self.order_by('pk'))[:1])
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 258, in __iter__
self._fetch_all()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1065, in _fetch_all
self._prefetch_related_objects()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 649, in
_prefetch_related_objects
prefetch_related_objects(self._result_cache,
self._prefetch_related_lookups)
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1437, in
prefetch_related_objects
obj_list, additional_lookups = prefetch_one_level(obj_list,
prefetcher, lookup, level)
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1536, in prefetch_one_level
prefetcher.get_prefetch_queryset(instances,
lookup.get_current_queryset(level)))
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/fields/related.py", line 753, in
get_prefetch_queryset
for rel_obj in queryset:
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 258, in __iter__
self._fetch_all()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1065, in _fetch_all
self._prefetch_related_objects()
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 649, in
_prefetch_related_objects
prefetch_related_objects(self._result_cache,
self._prefetch_related_lookups)
File "/home/gagaro/.virtualenvs/django-test/local/lib/python2.7/site-
packages/django/db/models/query.py", line 1426, in
prefetch_related_objects
(through_attr, first_obj.__class__.__name__, lookup.prefetch_through))
AttributeError: Cannot find 'b' on B object, 'b__c' is an invalid
parameter to prefetch_related()
}}}
I tested with Django 1.7, 1.8, 1.8.2 and master (commit
24718b7dccd64dfa118fe8136e7b175babec679b).
--
--
Ticket URL: <https://code.djangoproject.com/ticket/24873#comment:2>
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