diff options
| -rw-r--r-- | django/db/models/base.py | 1 | ||||
| -rw-r--r-- | django/db/models/query_utils.py | 5 | ||||
| -rw-r--r-- | docs/topics/db/queries.txt | 15 | ||||
| -rw-r--r-- | tests/defer_regress/tests.py | 22 | ||||
| -rw-r--r-- | tests/model_fields/test_generatedfield.py | 2 |
5 files changed, 42 insertions, 3 deletions
diff --git a/django/db/models/base.py b/django/db/models/base.py index 72ba0471a4..d4559e0693 100644 --- a/django/db/models/base.py +++ b/django/db/models/base.py @@ -859,6 +859,7 @@ class Model(AltersData, metaclass=ModelBase): not force_insert and deferred_non_generated_fields and using == self._state.db + and self._is_pk_set() ): field_names = set() pk_fields = self._meta.pk_fields diff --git a/django/db/models/query_utils.py b/django/db/models/query_utils.py index f0ae810f47..3e644a3c26 100644 --- a/django/db/models/query_utils.py +++ b/django/db/models/query_utils.py @@ -220,9 +220,10 @@ class DeferredAttribute: # might be able to reuse the already loaded value. Refs #18343. val = self._check_parent_chain(instance) if val is None: - if not instance._is_pk_set() and self.field.generated: + if not instance._is_pk_set(): raise AttributeError( - "Cannot read a generated field from an unsaved model." + f"Cannot retrieve deferred field {field_name!r} " + "from an unsaved model." ) instance.refresh_from_db(fields=[field_name]) else: diff --git a/docs/topics/db/queries.txt b/docs/topics/db/queries.txt index eb5b323abb..bd092f524b 100644 --- a/docs/topics/db/queries.txt +++ b/docs/topics/db/queries.txt @@ -1590,6 +1590,21 @@ For example, assuming ``entry`` is already duplicated as above:: detail.entry = entry detail.save() +Note that it is not possible to copy instances of models with deferred fields +using this pattern unless values are assigned to them: + +.. code-block:: pycon + + >>> blog = Blog.objects.defer("name")[0] + >>> blog.pk = None + >>> blog._state.adding = True + >>> blog.save() + Traceback (most recent call last): + ... + AttributeError: Cannot retrieve deferred field 'name' from an unsaved model. + >>> blog.name = "Another Blog" + >>> blog.save() + .. _topics-db-queries-update: Updating multiple objects at once diff --git a/tests/defer_regress/tests.py b/tests/defer_regress/tests.py index 1209325f21..c45a503630 100644 --- a/tests/defer_regress/tests.py +++ b/tests/defer_regress/tests.py @@ -366,3 +366,25 @@ class DeferDeletionSignalsTests(TestCase): Proxy.objects.only("value").get(pk=self.item_pk).delete() self.assertEqual(self.pre_delete_senders, [Proxy]) self.assertEqual(self.post_delete_senders, [Proxy]) + + +class DeferCopyInstanceTests(TestCase): + @classmethod + def setUpTestData(cls): + SimpleItem.objects.create(name="test", value=42) + cls.deferred_item = SimpleItem.objects.defer("value").first() + cls.deferred_item.pk = None + cls.deferred_item._state.adding = True + cls.expected_msg = ( + "Cannot retrieve deferred field 'value' from an unsaved model." + ) + + def test_save(self): + with self.assertRaisesMessage(AttributeError, self.expected_msg): + self.deferred_item.save(force_insert=True) + with self.assertRaisesMessage(AttributeError, self.expected_msg): + self.deferred_item.save() + + def test_bulk_create(self): + with self.assertRaisesMessage(AttributeError, self.expected_msg): + SimpleItem.objects.bulk_create([self.deferred_item]) diff --git a/tests/model_fields/test_generatedfield.py b/tests/model_fields/test_generatedfield.py index 9bc96a86bb..b6a933451d 100644 --- a/tests/model_fields/test_generatedfield.py +++ b/tests/model_fields/test_generatedfield.py @@ -180,7 +180,7 @@ class GeneratedFieldTestMixin: def test_unsaved_error(self): m = self.base_model(a=1, b=2) - msg = "Cannot read a generated field from an unsaved model." + msg = "Cannot retrieve deferred field 'field' from an unsaved model." with self.assertRaisesMessage(AttributeError, msg): m.field |