Ticket #27272: deletion.diff

django/db/models/deletion.py

@@ -78 +78 @@
         # parent.
         self.dependencies = {}  # {model: {models}}
 
+        self.protected_errors = []
+
     def add(self, objs, source=None, nullable=False, reverse_dependency=False):
         """
         Adds 'objs' to the collection of objects to be deleted.  If the call is
@@ -216 +218 @@
                     if self.can_fast_delete(sub_objs, from_field=field):
                         self.fast_deletes.append(sub_objs)
                     elif sub_objs:
-                        field.remote_field.on_delete(self, field, sub_objs, self.using)
+                        try:
+                            field.remote_field.on_delete(self, field, sub_objs, self.using)
+                        except ProtectedError as e:
+                            self.protected_errors.append(e)
+
             for field in model._meta.private_fields:
                 if hasattr(field, 'bulk_related_objects'):
                     # It's something like generic foreign key.
                     sub_objs = field.bulk_related_objects(new_objs, self.using)
                     self.collect(sub_objs, source=model, nullable=True)
 
+            for error in self.protected_errors:
+                not_deleted = [obj for obj in error.protected_objects if obj not in self.data.get(obj.__class__, [])]
+                candidate_fast_deletes = [qs for qs in self.fast_deletes if qs.model == error.protected_objects[0].__class__]
+
+                for obj in not_deleted:
+                    if not any(qs.filter(pk=obj.pk).exists() for qs in candidate_fast_deletes):
+                        raise error
+
     def related_objects(self, related, objs):
         """
         Gets a QuerySet of objects related to ``objs`` via the relation ``related``.