Re: [Django] #33312: Errors when trying to clone an object from a deferred queryset

[Django]

#33312: Errors when trying to clone an object from a deferred queryset
-+-
 Reporter:  Adam Sołtysik|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:
 |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Egor R):

 * cc: Egor R (added)


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[Django] #33312: Errors when trying to clone an object from a deferred queryset

[Django]

#33312: Errors when trying to clone an object from a deferred queryset
-+-
   Reporter:  Adam   |  Owner:  nobody
  Sołtysik   |
   Type:  Bug| Status:  new
  Component:  Database   |Version:  3.2
  layer (models, ORM)|
   Severity:  Normal |   Keywords:
   Triage Stage: |  Has patch:  0
  Unreviewed |
Needs documentation:  0  |Needs tests:  0
Patch needs improvement:  0  |  Easy pickings:  0
  UI/UX:  0  |
-+-
 As per [https://docs.djangoproject.com/en/3.2/topics/db/queries/#copying-
 model-instances documentation], it's possible to clone objects by setting
 `pk = None`.

 However, if the object to clone comes from a deferred queryset (after
 calling `defer` or `only`), trying to save the copy raises some hard to
 decipher exceptions.

 {{{
 class DeferCloneTest(TestCase):
 @classmethod
 def setUpTestData(cls):
 SimpleItem.objects.create(name="test", value=42)

 def _get_item(self):
 item = SimpleItem.objects.defer('value').first()  # same with
 `only` instead of `defer`
 item.pk = None
 item._state.adding = True  # doesn't seem to change anything
 return item

 def test_save(self):
 self._get_item().save()  # ValueError: Cannot force an update in
 save() with no primary key.

 def test_save_force_insert(self):
 self._get_item().save(force_insert=True)  #
 SimpleItem.DoesNotExist

 def test_bulk_create(self):
 SimpleItem.objects.bulk_create([self._get_item()])  #
 SimpleItem.DoesNotExist
 }}}

 Possibly related: #27419, #28019.

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