Refs #373 -- Added Model._is_pk_set() abstraction to check if a Model's PK is set.

django/contrib/contenttypes/forms.py

@@ -31,7 +31,7 @@ class BaseGenericInlineFormSet(BaseModelFormSet):
             + self.ct_fk_field.name
         )
         self.save_as_new = save_as_new
-        if self.instance is None or self.instance.pk is None:
+        if self.instance is None or not self.instance._is_pk_set():
             qs = self.model._default_manager.none()
         else:
             if queryset is None:

django/contrib/postgres/constraints.py

@@ -198,7 +198,7 @@ class ExclusionConstraint(BaseConstraint):
             lookups.append(lookup)
         queryset = queryset.filter(*lookups)
         model_class_pk = instance._get_pk_val(model._meta)
-        if not instance._state.adding and model_class_pk is not None:
+        if not instance._state.adding and instance._is_pk_set(model._meta):
             queryset = queryset.exclude(pk=model_class_pk)
         if not self.condition:
             if queryset.exists():

django/db/models/base.py

@@ -601,7 +601,7 @@ class Model(AltersData, metaclass=ModelBase):
         return my_pk == other.pk
 
     def __hash__(self):
-        if self.pk is None:
+        if not self._is_pk_set():
             raise TypeError("Model instances without primary key value are unhashable")
         return hash(self.pk)
 
@@ -662,6 +662,9 @@ class Model(AltersData, metaclass=ModelBase):
 
     pk = property(_get_pk_val, _set_pk_val)
 
+    def _is_pk_set(self, meta=None):
+        return self._get_pk_val(meta) is not None
+
     def get_deferred_fields(self):
         """
         Return a set containing names of deferred fields for this instance.
@@ -1094,11 +1097,10 @@ class Model(AltersData, metaclass=ModelBase):
                 if f.name in update_fields or f.attname in update_fields
             ]
 
-        pk_val = self._get_pk_val(meta)
+        if not self._is_pk_set(meta):
-        if pk_val is None:
             pk_val = meta.pk.get_pk_value_on_save(self)
             setattr(self, meta.pk.attname, pk_val)
-        pk_set = pk_val is not None
+        pk_set = self._is_pk_set(meta)
         if not pk_set and (force_update or update_fields):
             raise ValueError("Cannot force an update in save() with no primary key.")
         updated = False
@@ -1126,6 +1128,7 @@ class Model(AltersData, metaclass=ModelBase):
                 for f in non_pks_non_generated
             ]
             forced_update = update_fields or force_update
+            pk_val = self._get_pk_val(meta)
             updated = self._do_update(
                 base_qs, using, pk_val, values, update_fields, forced_update
             )
@@ -1226,7 +1229,7 @@ class Model(AltersData, metaclass=ModelBase):
                 # database to raise an IntegrityError if applicable. If
                 # constraints aren't supported by the database, there's the
                 # unavoidable risk of data corruption.
-                if obj.pk is None:
+                if not obj._is_pk_set():
                     # Remove the object from a related instance cache.
                     if not field.remote_field.multiple:
                         field.remote_field.delete_cached_value(obj)
@@ -1254,14 +1257,14 @@ class Model(AltersData, metaclass=ModelBase):
                 and hasattr(field, "fk_field")
             ):
                 obj = field.get_cached_value(self, default=None)
-                if obj and obj.pk is None:
+                if obj and not obj._is_pk_set():
                     raise ValueError(
                         f"{operation_name}() prohibited to prevent data loss due to "
                         f"unsaved related object '{field.name}'."
                     )
 
     def delete(self, using=None, keep_parents=False):
-        if self.pk is None:
+        if not self._is_pk_set():
             raise ValueError(
                 "%s object can't be deleted because its %s attribute is set "
                 "to None." % (self._meta.object_name, self._meta.pk.attname)
@@ -1367,7 +1370,7 @@ class Model(AltersData, metaclass=ModelBase):
         return field_map
 
     def prepare_database_save(self, field):
-        if self.pk is None:
+        if not self._is_pk_set():
             raise ValueError(
                 "Unsaved model instance %r cannot be used in an ORM query." % self
             )
@@ -1497,7 +1500,7 @@ class Model(AltersData, metaclass=ModelBase):
             # allows single model to have effectively multiple primary keys.
             # Refs #17615.
             model_class_pk = self._get_pk_val(model_class._meta)
-            if not self._state.adding and model_class_pk is not None:
+            if not self._state.adding and self._is_pk_set(model_class._meta):
                 qs = qs.exclude(pk=model_class_pk)
             if qs.exists():
                 if len(unique_check) == 1:
@@ -1532,7 +1535,7 @@ class Model(AltersData, metaclass=ModelBase):
             qs = model_class._default_manager.filter(**lookup_kwargs)
             # Exclude the current object from the query if we are editing an
             # instance (as opposed to creating a new one)
-            if not self._state.adding and self.pk is not None:
+            if not self._state.adding and self._is_pk_set():
                 qs = qs.exclude(pk=self.pk)
 
             if qs.exists():

django/db/models/constraints.py

@@ -686,7 +686,7 @@ class UniqueConstraint(BaseConstraint):
                 filters.append(condition)
             queryset = queryset.filter(*filters)
         model_class_pk = instance._get_pk_val(model._meta)
-        if not instance._state.adding and model_class_pk is not None:
+        if not instance._state.adding and instance._is_pk_set(model._meta):
             queryset = queryset.exclude(pk=model_class_pk)
         if not self.condition:
             if queryset.exists():

django/db/models/fields/related.py

@@ -1969,7 +1969,7 @@ class ManyToManyField(RelatedField):
         pass
 
     def value_from_object(self, obj):
-        return [] if obj.pk is None else list(getattr(obj, self.attname).all())
+        return list(getattr(obj, self.attname).all()) if obj._is_pk_set() else []
 
     def save_form_data(self, instance, data):
         getattr(instance, self.attname).set(data)

django/db/models/fields/related_descriptors.py

@@ -511,8 +511,7 @@ class ReverseOneToOneDescriptor:
         try:
             rel_obj = self.related.get_cached_value(instance)
         except KeyError:
-            related_pk = instance.pk
+            if not instance._is_pk_set():
-            if related_pk is None:
                 rel_obj = None
             else:
                 filter_args = self.related.field.get_forward_related_filter(instance)
@@ -753,7 +752,7 @@ def create_reverse_many_to_one_manager(superclass, rel):
             # Even if this relation is not to pk, we require still pk value.
             # The wish is that the instance has been already saved to DB,
             # although having a pk value isn't a guarantee of that.
-            if self.instance.pk is None:
+            if not self.instance._is_pk_set():
                 raise ValueError(
                     f"{self.instance.__class__.__name__!r} instance needs to have a "
                     f"primary key value before this relationship can be used."
@@ -1081,7 +1080,7 @@ def create_forward_many_to_many_manager(superclass, rel, reverse):
             # Even if this relation is not to pk, we require still pk value.
             # The wish is that the instance has been already saved to DB,
             # although having a pk value isn't a guarantee of that.
-            if instance.pk is None:
+            if not instance._is_pk_set():
                 raise ValueError(
                     "%r instance needs to have a primary key value before "
                     "a many-to-many relationship can be used."

django/db/models/fields/related_lookups.py

@@ -16,7 +16,7 @@ def get_normalized_value(value, lhs):
     from django.db.models import Model
 
     if isinstance(value, Model):
-        if value.pk is None:
+        if not value._is_pk_set():
             raise ValueError("Model instances passed to related filters must be saved.")
         value_list = []
         sources = lhs.output_field.path_infos[-1].target_fields

django/db/models/query.py

@@ -668,7 +668,7 @@ class QuerySet(AltersData):
 
         connection = connections[self.db]
         for obj in objs:
-            if obj.pk is None:
+            if not obj._is_pk_set():
                 # Populate new PK values.
                 obj.pk = obj._meta.pk.get_pk_value_on_save(obj)
             if not connection.features.supports_default_keyword_in_bulk_insert:
@@ -794,7 +794,7 @@ class QuerySet(AltersData):
         objs = list(objs)
         self._prepare_for_bulk_create(objs)
         with transaction.atomic(using=self.db, savepoint=False):
-            objs_with_pk, objs_without_pk = partition(lambda o: o.pk is None, objs)
+            objs_without_pk, objs_with_pk = partition(lambda o: o._is_pk_set(), objs)
             if objs_with_pk:
                 returned_columns = self._batched_insert(
                     objs_with_pk,
@@ -862,7 +862,7 @@ class QuerySet(AltersData):
         if not fields:
             raise ValueError("Field names must be given to bulk_update().")
         objs = tuple(objs)
-        if any(obj.pk is None for obj in objs):
+        if not all(obj._is_pk_set() for obj in objs):
             raise ValueError("All bulk_update() objects must have a primary key set.")
         fields = [self.model._meta.get_field(name) for name in fields]
         if any(not f.concrete or f.many_to_many for f in fields):
@@ -1289,7 +1289,7 @@ class QuerySet(AltersData):
                 return False
         except AttributeError:
             raise TypeError("'obj' must be a model instance.")
-        if obj.pk is None:
+        if not obj._is_pk_set():
             raise ValueError("QuerySet.contains() cannot be used on unsaved objects.")
         if self._result_cache is not None:
             return obj in self._result_cache

django/db/models/query_utils.py

@@ -220,7 +220,7 @@ class DeferredAttribute:
             # might be able to reuse the already loaded value. Refs #18343.
             val = self._check_parent_chain(instance)
             if val is None:
-                if instance.pk is None and self.field.generated:
+                if not instance._is_pk_set() and self.field.generated:
                     raise AttributeError(
                         "Cannot read a generated field from an unsaved model."
                     )

django/forms/models.py

@@ -935,7 +935,7 @@ class BaseModelFormSet(BaseFormSet, AltersData):
             # 1. The object is an unexpected empty model, created by invalid
             #    POST data such as an object outside the formset's queryset.
             # 2. The object was already deleted from the database.
-            if obj.pk is None:
+            if not obj._is_pk_set():
                 continue
             if form in forms_to_delete:
                 self.deleted_objects.append(obj)
@@ -1103,7 +1103,7 @@ class BaseInlineFormSet(BaseModelFormSet):
         self.save_as_new = save_as_new
         if queryset is None:
             queryset = self.model._default_manager
-        if self.instance.pk is not None:
+        if self.instance._is_pk_set():
             qs = queryset.filter(**{self.fk.name: self.instance})
         else:
             qs = queryset.none()

docs/ref/models/instances.txt

@@ -973,3 +973,14 @@ Other attributes
     since they are yet to be saved. Instances fetched from a ``QuerySet``
     will have ``adding=False`` and ``db`` set to the alias of the associated
     database.
+
+``_is_pk_set()``
+----------------
+
+.. method:: Model._is_pk_set()
+
+.. versionadded:: 5.2
+
+The ``_is_pk_set()`` method returns whether the model instance's ``pk`` is set.
+It abstracts the model's primary key definition, ensuring consistent behavior
+regardless of the specific ``pk`` configuration.

docs/releases/5.2.txt

@@ -289,7 +289,9 @@ Database backend API
 This section describes changes that may be needed in third-party database
 backends.
 
-* ...
+* The new :meth:`Model._is_pk_set() <django.db.models.Model._is_pk_set>` method
+  allows checking if a Model instance's primary key is defined.
+
 
 :mod:`django.contrib.gis`
 -------------------------

tests/basic/tests.py

@@ -661,6 +661,31 @@ class ModelTest(TestCase):
             headline__startswith="Area",
         )
 
+    def test_is_pk_unset(self):
+        cases = [
+            Article(),
+            Article(id=None),
+        ]
+        for case in cases:
+            with self.subTest(case=case):
+                self.assertIs(case._is_pk_set(), False)
+
+    def test_is_pk_set(self):
+        def new_instance():
+            a = Article(pub_date=datetime.today())
+            a.save()
+            return a
+
+        cases = [
+            Article(id=1),
+            Article(id=0),
+            Article.objects.create(pub_date=datetime.today()),
+            new_instance(),
+        ]
+        for case in cases:
+            with self.subTest(case=case):
+                self.assertIs(case._is_pk_set(), True)
+
 
 class ModelLookupTest(TestCase):
     @classmethod