From a23a0f2708cd3c62b729c4caf4fe72e9906984a1 Mon Sep 17 00:00:00 2001
From: Arthur <worldnomad@gmail.com>
Date: Fri, 6 Jun 2025 15:18:55 -0700
Subject: [PATCH] #19680 fix deletion dependency order for GenericRelations

---
 netbox/dcim/models/devices.py    |   4 +-
 netbox/netbox/models/deletion.py | 117 +++++++++++++++++++++++++++++++
 2 files changed, 120 insertions(+), 1 deletion(-)
 create mode 100644 netbox/netbox/models/deletion.py

diff --git a/netbox/dcim/models/devices.py b/netbox/dcim/models/devices.py
index 5988f8241..ae0b9fffe 100644
--- a/netbox/dcim/models/devices.py
+++ b/netbox/dcim/models/devices.py
@@ -25,6 +25,7 @@ from extras.querysets import ConfigContextModelQuerySet
 from netbox.choices import ColorChoices
 from netbox.config import ConfigItem
 from netbox.models import NestedGroupModel, OrganizationalModel, PrimaryModel
+from netbox.models.deletion import DeleteMixin
 from netbox.models.mixins import WeightMixin
 from netbox.models.features import ContactsMixin, ImageAttachmentsMixin
 from utilities.fields import ColorField, CounterCacheField
@@ -430,12 +431,13 @@ class Platform(OrganizationalModel):
 
 
 class Device(
+    DeleteMixin,
     ContactsMixin,
     ImageAttachmentsMixin,
     RenderConfigMixin,
     ConfigContextModel,
     TrackingModelMixin,
-    PrimaryModel
+    PrimaryModel,
 ):
     """
     A Device represents a piece of physical hardware mounted within a Rack. Each Device is assigned a DeviceType,
diff --git a/netbox/netbox/models/deletion.py b/netbox/netbox/models/deletion.py
new file mode 100644
index 000000000..006c49c1e
--- /dev/null
+++ b/netbox/netbox/models/deletion.py
@@ -0,0 +1,117 @@
+import logging
+
+from django.contrib.contenttypes.fields import GenericRelation
+from django.db import router
+from django.db.models.deletion import Collector
+
+logger = logging.getLogger("netbox.models.deletion")
+
+
+class CustomCollector(Collector):
+    """
+    Custom collector that handles GenericRelations correctly.
+    """
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self._processed_objects = set()
+
+    def collect(
+        self,
+        objs,
+        source=None,
+        nullable=False,
+        collect_related=True,
+        source_attr=None,
+        reverse_dependency=False,
+        keep_parents=False,
+        fail_on_restricted=True,
+    ):
+        """
+        Override collect to first collect standard dependencies,
+        then add GenericRelations to the dependency graph.
+        """
+        # Filter out objects we've already processed
+        new_objs = []
+        for obj in objs:
+            obj_key = f"{obj._meta.model_name}.{obj.pk}"
+            if obj_key not in self._processed_objects:
+                self._processed_objects.add(obj_key)
+                new_objs.append(obj)
+
+        if not new_objs:
+            return
+
+        # Call parent collect first to get all standard dependencies
+        super().collect(
+            new_objs,
+            source=source,
+            nullable=nullable,
+            collect_related=collect_related,
+            source_attr=source_attr,
+            reverse_dependency=reverse_dependency,
+            keep_parents=keep_parents,
+            fail_on_restricted=fail_on_restricted,
+        )
+
+        # Track which GenericRelations we've already processed to prevent infinite recursion
+        processed_relations = set()
+
+        # Now add GenericRelations to the dependency graph
+        for _, instances in list(self.data.items()):
+            for instance in instances:
+                # Get all GenericRelations for this model
+                for field in instance._meta.private_fields:
+                    if isinstance(field, GenericRelation):
+                        # Create a unique key for this relation
+                        relation_key = f"{instance._meta.model_name}.{field.name}"
+                        if relation_key in processed_relations:
+                            continue
+                        processed_relations.add(relation_key)
+
+                        # Get the related objects
+                        related_objs = getattr(instance, field.name).all()
+                        if related_objs:
+                            # Add them to the dependency graph
+                            self.collect(
+                                related_objs,
+                                source=instance,
+                                nullable=True,
+                                collect_related=True,
+                                source_attr=field.name,
+                                reverse_dependency=True,
+                                keep_parents=keep_parents,
+                                fail_on_restricted=False,
+                            )
+
+
+class DeleteMixin:
+    """
+    Mixin to override the model delete function to use our custom collector.
+    """
+
+    def delete(self, using=None, keep_parents=False):
+        """
+        Override delete to use our custom collector.
+        """
+        using = using or router.db_for_write(self.__class__, instance=self)
+        assert self._get_pk_val() is not None, "%s object can't be deleted because its %s attribute is set to None." % (
+            self._meta.object_name,
+            self._meta.pk.attname,
+        )
+
+        collector = CustomCollector(using=using)
+        collector.collect([self], keep_parents=keep_parents)
+
+        return collector.delete()
+
+    delete.alters_data = True
+
+    @classmethod
+    def verify_mro(cls, instance):
+        """
+        Verify that this mixin is first in the MRO.
+        """
+        mro = instance.__class__.__mro__
+        if mro.index(cls) != 0:
+            raise RuntimeError(f"{cls.__name__} must be first in the MRO. Current MRO: {mro}")