When updating an instance with foreign key relations, the objects linking to the instance should not be deleted. Instead, the foreign key should simply be removed from the objects to the instance. This commit checks if the related field is a foreign key, and, if so, it unlinks the object. If the field cannot be null, the object gets deleted.

Author: gibsonbailey

drf_writable_nested/mixins.py

@@ -333,6 +333,12 @@ def delete_reverse_relations_if_need(self, instance, reverse_relations):
                     # Remove relations from m2m table
                     m2m_manager = getattr(instance, field_source)
                     m2m_manager.remove(*pks_to_delete)
+                elif related_field.many_to_one and related_field.null:
+                    # The instance should not be deleted if the object is foreign-key related.
+                    unlink_foreign_key = {
+                        related_field.name: None,
+                    }
+                    model_class.objects.filter(pk__in=pks_to_delete).update(**unlink_foreign_key)
                 else:
                     model_class.objects.filter(pk__in=pks_to_delete).delete()