Fix #19524 -- Incorrect caching of parents of unsaved model instances.

Thanks qcwxezdas for the report. Refs #13839.

django/db/models/base.py

@@ -583,6 +583,15 @@ class Model(six.with_metaclass(ModelBase, object)):
 
                 if field:
                     setattr(self, field.attname, self._get_pk_val(parent._meta))
+                    # Since we didn't have an instance of the parent handy, we
+                    # set attname directly, bypassing the descriptor.
+                    # Invalidate the related object cache, in case it's been
+                    # accidentally populated. A fresh instance will be
+                    # re-built from the database if necessary.
+                    cache_name = field.get_cache_name()
+                    if hasattr(self, cache_name):
+                        delattr(self, cache_name)
+
             if meta.proxy:
                 return
 

django/forms/models.py

@@ -692,7 +692,10 @@ class BaseInlineFormSet(BaseModelFormSet):
         self.rel_name = RelatedObject(self.fk.rel.to, self.model, self.fk).get_accessor_name()
         if queryset is None:
             queryset = self.model._default_manager
-        qs = queryset.filter(**{self.fk.name: self.instance})
+        if self.instance.pk:
+            qs = queryset.filter(**{self.fk.name: self.instance})
+        else:
+            qs = queryset.none()
         super(BaseInlineFormSet, self).__init__(data, files, prefix=prefix,
                                                 queryset=qs, **kwargs)