17558 raise validation error if removing used choice from ChoiceSet (#17591)

* 17558 raise validation error if removing choice from choiceset that is currently used

* 17558 raise validation error if removing choice from choiceset that is currently used

* 17558 raise validation error if removing choice from choiceset that is currently used

* 17558 add tests

* 17558 add tests

* Tightened up choice evaluation logic a bit; cleaned up test

---------

Co-authored-by: Jeremy Stretch <jstretch@netboxlabs.com>

netbox/extras/models/customfields.py

@@ -785,6 +785,12 @@ class CustomFieldChoiceSet(CloningMixin, ExportTemplatesMixin, ChangeLoggedModel
     def __str__(self):
         return self.name
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        # Cache the initial set of choices for comparison under clean()
+        self._original_extra_choices = self.__dict__.get('extra_choices')
+
     def get_absolute_url(self):
         return reverse('extras:customfieldchoiceset', args=[self.pk])
 
@@ -818,6 +824,32 @@ class CustomFieldChoiceSet(CloningMixin, ExportTemplatesMixin, ChangeLoggedModel
         if not self.base_choices and not self.extra_choices:
             raise ValidationError(_("Must define base or extra choices."))
 
+        # Check whether any choices have been removed. If so, check whether any of the removed
+        # choices are still set in custom field data for any object.
+        original_choices = set([
+            c[0] for c in self._original_extra_choices
+        ]) if self._original_extra_choices else set()
+        current_choices = set([
+            c[0] for c in self.extra_choices
+        ]) if self.extra_choices else set()
+        if removed_choices := original_choices - current_choices:
+            for custom_field in self.choices_for.all():
+                for object_type in custom_field.object_types.all():
+                    model = object_type.model_class()
+                    for choice in removed_choices:
+                        # Form the query based on the type of custom field
+                        if custom_field.type == CustomFieldTypeChoices.TYPE_MULTISELECT:
+                            query_args = {f"custom_field_data__{custom_field.name}__contains": choice}
+                        else:
+                            query_args = {f"custom_field_data__{custom_field.name}": choice}
+                        # Raise a ValidationError if there are any objects which still reference the removed choice
+                        if model.objects.filter(models.Q(**query_args)).exists():
+                            raise ValidationError(
+                                _(
+                                    "Cannot remove choice {choice} as there are {model} objects which reference it."
+                                ).format(choice=choice, model=object_type)
+                            )
+
     def save(self, *args, **kwargs):
 
         # Sort choices if alphabetical ordering is enforced

netbox/extras/tests/test_customfields.py

@@ -343,6 +343,74 @@ class CustomFieldTest(TestCase):
         instance.refresh_from_db()
         self.assertIsNone(instance.custom_field_data.get(cf.name))
 
+    def test_remove_selected_choice(self):
+        """
+        Removing a ChoiceSet choice that is referenced by an object should raise
+        a ValidationError exception.
+        """
+        CHOICES = (
+            ('a', 'Option A'),
+            ('b', 'Option B'),
+            ('c', 'Option C'),
+            ('d', 'Option D'),
+        )
+
+        # Create a set of custom field choices
+        choice_set = CustomFieldChoiceSet.objects.create(
+            name='Custom Field Choice Set 1',
+            extra_choices=CHOICES
+        )
+
+        # Create a select custom field
+        cf = CustomField.objects.create(
+            name='select_field',
+            type=CustomFieldTypeChoices.TYPE_SELECT,
+            required=False,
+            choice_set=choice_set
+        )
+        cf.object_types.set([self.object_type])
+
+        # Create a multi-select custom field
+        cf_multiselect = CustomField.objects.create(
+            name='multiselect_field',
+            type=CustomFieldTypeChoices.TYPE_MULTISELECT,
+            required=False,
+            choice_set=choice_set
+        )
+        cf_multiselect.object_types.set([self.object_type])
+
+        # Assign a choice for both custom fields on an object
+        instance = Site.objects.first()
+        instance.custom_field_data[cf.name] = 'a'
+        instance.custom_field_data[cf_multiselect.name] = ['b', 'c']
+        instance.save()
+
+        # Attempting to delete a selected choice should fail
+        with self.assertRaises(ValidationError):
+            choice_set.extra_choices = (
+                ('b', 'Option B'),
+                ('c', 'Option C'),
+                ('d', 'Option D'),
+            )
+            choice_set.full_clean()
+
+        # Attempting to delete either of the multi-select choices should fail
+        with self.assertRaises(ValidationError):
+            choice_set.extra_choices = (
+                ('a', 'Option A'),
+                ('b', 'Option B'),
+                ('d', 'Option D'),
+            )
+            choice_set.full_clean()
+
+        # Removing a non-selected choice should succeed
+        choice_set.extra_choices = (
+            ('a', 'Option A'),
+            ('b', 'Option B'),
+            ('c', 'Option C'),
+        )
+        choice_set.full_clean()
+
     def test_object_field(self):
         value = VLAN.objects.create(name='VLAN 1', vid=1).pk