Fixes #11460 - Fix unterminated cable exception when editing cable (#15813)

* Fix cable edit form with single unterminated cable

* Minor tweaks

* Instead of skipping HTMX, override the template & move form template to an "htmx" template

* Use HTMXSelect widget for A/B type selection

* Infer A/B termination types from POST data

* Fix saving cable which results in resetting of the termination type fields

* Condense view logic

---------

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

netbox/dcim/forms/connections.py

@@ -1,4 +1,5 @@
 from django import forms
+from django.contrib.contenttypes.models import ContentType
 from django.utils.translation import gettext_lazy as _
 
 from circuits.models import Circuit, CircuitTermination
@@ -82,14 +83,22 @@ def get_cable_form(a_type, b_type):
 
     class _CableForm(CableForm, metaclass=FormMetaclass):
 
-        def __init__(self, *args, **kwargs):
+        def __init__(self, *args, initial=None, **kwargs):
+
+            initial = initial or {}
+            if a_type:
+                ct = ContentType.objects.get_for_model(a_type)
+                initial['a_terminations_type'] = f'{ct.app_label}.{ct.model}'
+            if b_type:
+                ct = ContentType.objects.get_for_model(b_type)
+                initial['b_terminations_type'] = f'{ct.app_label}.{ct.model}'
 
             # TODO: Temporary hack to work around list handling limitations with utils.normalize_querydict()
             for field_name in ('a_terminations', 'b_terminations'):
-                if field_name in kwargs.get('initial', {}) and type(kwargs['initial'][field_name]) is not list:
-                    kwargs['initial'][field_name] = [kwargs['initial'][field_name]]
+                if field_name in initial and type(initial[field_name]) is not list:
+                    initial[field_name] = [initial[field_name]]
 
-            super().__init__(*args, **kwargs)
+            super().__init__(*args, initial=initial, **kwargs)
 
             if self.instance and self.instance.pk:
                 # Initialize A/B terminations when modifying an existing Cable instance
@@ -100,7 +109,7 @@ def get_cable_form(a_type, b_type):
             super().clean()
 
             # Set the A/B terminations on the Cable instance
-            self.instance.a_terminations = self.cleaned_data['a_terminations']
-            self.instance.b_terminations = self.cleaned_data['b_terminations']
+            self.instance.a_terminations = self.cleaned_data.get('a_terminations', [])
+            self.instance.b_terminations = self.cleaned_data.get('b_terminations', [])
 
     return _CableForm

netbox/dcim/forms/model_forms.py

@@ -13,8 +13,7 @@ from netbox.forms import NetBoxModelForm
 from tenancy.forms import TenancyForm
 from utilities.forms import BootstrapMixin, add_blank_choice
 from utilities.forms.fields import (
-    CommentField, ContentTypeChoiceField, DynamicModelChoiceField, DynamicModelMultipleChoiceField, JSONField,
-    NumericArrayField, SlugField,
+    CommentField, DynamicModelChoiceField, DynamicModelMultipleChoiceField, JSONField, NumericArrayField, SlugField,
 )
 from utilities.forms.widgets import APISelect, ClearableFileInput, HTMXSelect, NumberWithOptions, SelectWithPK
 from virtualization.models import Cluster
@@ -616,14 +615,33 @@ class ModuleForm(ModuleCommonForm, NetBoxModelForm):
             self.fields['adopt_components'].disabled = True
 
 
+def get_termination_type_choices():
+    return add_blank_choice([
+        (f'{ct.app_label}.{ct.model}', ct.model_class()._meta.verbose_name.title())
+        for ct in ContentType.objects.filter(CABLE_TERMINATION_MODELS)
+    ])
+
+
 class CableForm(TenancyForm, NetBoxModelForm):
+    a_terminations_type = forms.ChoiceField(
+        choices=get_termination_type_choices,
+        required=False,
+        widget=HTMXSelect(),
+        label=_('Type')
+    )
+    b_terminations_type = forms.ChoiceField(
+        choices=get_termination_type_choices,
+        required=False,
+        widget=HTMXSelect(),
+        label=_('Type')
+    )
     comments = CommentField()
 
     class Meta:
         model = Cable
         fields = [
-            'type', 'status', 'tenant_group', 'tenant', 'label', 'color', 'length', 'length_unit', 'description',
-            'comments', 'tags',
+            'a_terminations_type', 'b_terminations_type', 'type', 'status', 'tenant_group', 'tenant', 'label', 'color',
+            'length', 'length_unit', 'description', 'comments', 'tags',
         ]
         error_messages = {
             'length': {