Merge pull request #485 from netboxlabs/471-object-field-on-delete-behavior

Closes: #471 -  selectable on_delete behavior for Object-type fields

Author: bctiemann

netbox_custom_objects/api/serializers.py

@@ -68,6 +68,7 @@ class Meta:
             "related_object_type",
             "related_object_filter",
             "related_name",
+            "on_delete_behavior",
             "app_label",
             "model",
             "group_name",
@@ -123,8 +124,19 @@ def validate(self, attrs):
                 raise ValidationError(
                     "Must provide choice_set with valid PK for select field type."
                 )
+        on_delete = attrs.get("on_delete_behavior")
+        if on_delete and field_type and field_type != CustomFieldTypeChoices.TYPE_OBJECT:
+            raise ValidationError(
+                {"on_delete_behavior": "on_delete_behavior can only be set for Object-type fields."}
+            )
         return super().validate(attrs)
 
+    def to_representation(self, instance):
+        data = super().to_representation(instance)
+        if instance.type != CustomFieldTypeChoices.TYPE_OBJECT:
+            data['on_delete_behavior'] = None
+        return data
+
     def create(self, validated_data):
         """
         Record the user who created the Custom Object as its owner.

netbox_custom_objects/choices.py

@@ -2,6 +2,19 @@
 from utilities.choices import ChoiceSet
 
 
+class ObjectFieldOnDeleteChoices(ChoiceSet):
+    """Controls what happens to a Custom Object when the referenced object is deleted."""
+    CASCADE = "cascade"
+    SET_NULL = "set_null"
+    PROTECT = "protect"
+
+    CHOICES = (
+        (SET_NULL, _("Set null (clear the field, keep this object)")),
+        (CASCADE, _("Cascade (delete this object too)")),
+        (PROTECT, _("Protect (prevent deletion of the referenced object)")),
+    )
+
+
 class MappingFieldTypeChoices(ChoiceSet):
     CHAR = "char"
     INTEGER = "integer"

netbox_custom_objects/field_types.py

@@ -29,6 +29,7 @@
 from utilities.templatetags.builtins.filters import linkify, render_markdown
 from netbox.tables.columns import BooleanColumn
 
+from netbox_custom_objects.choices import ObjectFieldOnDeleteChoices
 from netbox_custom_objects.constants import APP_LABEL
 from netbox_custom_objects.utilities import extract_cot_id_from_model_name, generate_model
 
@@ -486,6 +487,13 @@ def render_table_column(self, value):
         return ", ".join(value)
 
 
+_ON_DELETE_MAP = {
+    ObjectFieldOnDeleteChoices.CASCADE: models.CASCADE,
+    ObjectFieldOnDeleteChoices.SET_NULL: models.SET_NULL,
+    ObjectFieldOnDeleteChoices.PROTECT: models.PROTECT,
+}
+
+
 class ObjectFieldType(FieldType):
     def get_model_field(self, field, **kwargs):
         content_type = self._get_related_content_type(field)
@@ -495,6 +503,11 @@ def get_model_field(self, field, **kwargs):
         field_kwargs = {k: v for k, v in kwargs.items() if not k.startswith('_')}
         field_kwargs.update({"default": field.default, "unique": field.unique})
 
+        on_delete = _ON_DELETE_MAP.get(
+            getattr(field, 'on_delete_behavior', None) or ObjectFieldOnDeleteChoices.SET_NULL,
+            models.SET_NULL,
+        )
+
         # Handle self-referential fields by using string references
         if content_type.app_label == APP_LABEL:
             from netbox_custom_objects.models import CustomObjectType
@@ -522,7 +535,7 @@ def get_model_field(self, field, **kwargs):
                     model_name,
                     null=True,
                     blank=True,
-                    on_delete=models.SET_NULL,
+                    on_delete=on_delete,
                     related_name=related_name,
                     **field_kwargs
                 )
@@ -542,7 +555,7 @@ def get_model_field(self, field, **kwargs):
             table_model_name = field.custom_object_type.get_table_model_name(field.custom_object_type.id).lower()
             related_name = f"{table_model_name}_{field.name}_set"
         f = models.ForeignKey(
-            model, null=True, blank=True, on_delete=models.SET_NULL, related_name=related_name, **field_kwargs
+            model, null=True, blank=True, on_delete=on_delete, related_name=related_name, **field_kwargs
         )
 
         return f

netbox_custom_objects/forms.py

@@ -7,6 +7,7 @@
 from utilities.forms.fields import (CommentField, ContentTypeChoiceField,
                                     DynamicModelChoiceField, SlugField, TagFilterField)
 from utilities.forms.rendering import FieldSet
+from utilities.forms.utils import get_field_value
 from utilities.object_types import object_type_name
 
 from netbox_custom_objects.choices import SearchWeightChoices
@@ -187,21 +188,28 @@ def __init__(self, *args, **kwargs):
                 self.fields["related_object_type"].disabled = True
 
         # Multi-object fields may not be set unique
-        if self.initial["type"] == CustomFieldTypeChoices.TYPE_MULTIOBJECT:
+        if get_field_value(self, 'type') == CustomFieldTypeChoices.TYPE_MULTIOBJECT:
             self.fields["unique"].disabled = True
 
-        # Add related_name to the Related Object fieldset for object/multiobject fields.
-        # The parent CustomFieldForm.__init__ removes related_object_type from self.fields
-        # for non-object types, so we use its presence as a signal.
+        # Add related_name (and on_delete_behavior for single-object fields) to the
+        # Related Object fieldset.  The parent CustomFieldForm.__init__ removes
+        # related_object_type from self.fields for non-object types, so we use its
+        # presence as a signal.
         if "related_object_type" in self.fields:
+            field_type = get_field_value(self, 'type')
+            is_single_object = field_type == CustomFieldTypeChoices.TYPE_OBJECT
+            extra = ("related_name", "on_delete_behavior") if is_single_object else ("related_name",)
             self.fieldsets = tuple(
-                FieldSet(*fs.items, "related_name", name=fs.name)
+                FieldSet(*fs.items, *extra, name=fs.name)
                 if "related_object_type" in fs.items
                 else fs
                 for fs in self.fieldsets
             )
+            if not is_single_object:
+                del self.fields["on_delete_behavior"]
         else:
             del self.fields["related_name"]
+            del self.fields["on_delete_behavior"]
 
     def clean_primary(self):
         primary_fields = self.cleaned_data["custom_object_type"].fields.filter(

netbox_custom_objects/migrations/0011_customobjecttypefield_on_delete_behavior.py

@@ -0,0 +1,33 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("netbox_custom_objects", "0010_fix_object_fk_set_null"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="customobjecttypefield",
+            name="on_delete_behavior",
+            field=models.CharField(
+                blank=True,
+                choices=[
+                    ("set_null", "Set null (clear the field, keep this object)"),
+                    ("cascade", "Cascade (delete this object too)"),
+                    ("protect", "Protect (prevent deletion of the referenced object)"),
+                ],
+                default="set_null",
+                help_text=(
+                    "What happens to this Custom Object when the referenced object is deleted "
+                    "(applies to Object-type fields only). "
+                    "Set null: clear the field and keep this object. "
+                    "Cascade: delete this object too. "
+                    "Protect: prevent deletion of the referenced object."
+                ),
+                max_length=20,
+                verbose_name="on delete behavior",
+            ),
+        ),
+    ]