12328 update GFK object in clean (#13946)

* 12328 update GFK object in clean

* Add missing import statement

---------

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

netbox/netbox/models/__init__.py

@@ -1,5 +1,6 @@
 from django.conf import settings
 from django.contrib.contenttypes.fields import GenericForeignKey
+from django.core.exceptions import ObjectDoesNotExist
 from django.core.validators import ValidationError
 from django.db import models
 from django.utils.translation import gettext_lazy as _
@@ -85,11 +86,16 @@ class NetBoxModel(NetBoxFeatureSet, models.Model):
 
                 if ct_value and fk_value:
                     klass = getattr(self, field.ct_field).model_class()
-                    if not klass.objects.filter(pk=fk_value).exists():
+                    try:
+                        obj = klass.objects.get(pk=fk_value)
+                    except ObjectDoesNotExist:
                         raise ValidationError({
                             field.fk_field: f"Related object not found using the provided value: {fk_value}."
                         })
 
+                    # update the GFK field value
+                    setattr(self, field.name, obj)
+
 
 #
 # NetBox internal base models