Closes netbox-community#893: Allow filtering by null values for NullC…

…haracterFields (e.g. return only unnamed devices)

netbox/dcim/filters.py

@@ -8,7 +8,7 @@
 
 from extras.filters import CustomFieldFilterSet
 from tenancy.models import Tenant
-from utilities.filters import NullableModelMultipleChoiceFilter, NumericInFilter
+from utilities.filters import NullableCharFieldFilter, NullableModelMultipleChoiceFilter, NumericInFilter
 from .models import (
     ConsolePort, ConsolePortTemplate, ConsoleServerPort, ConsoleServerPortTemplate, Device, DeviceBay,
     DeviceBayTemplate, DeviceRole, DeviceType, STATUS_CHOICES, IFACE_FF_LAG, Interface, InterfaceConnection,
@@ -113,6 +113,7 @@ class RackFilter(CustomFieldFilterSet, django_filters.FilterSet):
         method='search',
         label='Search',
     )
+    facility_id = NullableCharFieldFilter()
     site_id = django_filters.ModelMultipleChoiceFilter(
         queryset=Site.objects.all(),
         label='Site (ID)',
@@ -156,7 +157,7 @@ class RackFilter(CustomFieldFilterSet, django_filters.FilterSet):
 
     class Meta:
         model = Rack
-        fields = ['facility_id', 'type', 'width', 'u_height', 'desc_units']
+        fields = ['type', 'width', 'u_height', 'desc_units']
 
     def search(self, queryset, name, value):
         if not value.strip():
@@ -383,6 +384,8 @@ class DeviceFilter(CustomFieldFilterSet, django_filters.FilterSet):
         to_field_name='slug',
         label='Platform (slug)',
     )
+    name = NullableCharFieldFilter()
+    asset_tag = NullableCharFieldFilter()
     site_id = django_filters.ModelMultipleChoiceFilter(
         queryset=Site.objects.all(),
         label='Site (ID)',
@@ -439,7 +442,7 @@ class DeviceFilter(CustomFieldFilterSet, django_filters.FilterSet):
 
     class Meta:
         model = Device
-        fields = ['name', 'serial', 'asset_tag']
+        fields = ['serial']
 
     def search(self, queryset, name, value):
         if not value.strip():
@@ -596,10 +599,11 @@ class InventoryItemFilter(DeviceComponentFilterSet):
         to_field_name='slug',
         label='Manufacturer (slug)',
     )
+    asset_tag = NullableCharFieldFilter()
 
     class Meta:
         model = InventoryItem
-        fields = ['name', 'part_id', 'serial', 'asset_tag', 'discovered']
+        fields = ['name', 'part_id', 'serial', 'discovered']
 
 
 class ConsoleConnectionFilter(django_filters.FilterSet):

netbox/utilities/filters.py

@@ -19,6 +19,16 @@ class NumericInFilter(django_filters.BaseInFilter, django_filters.NumberFilter):
     pass
 
 
+class NullableCharFieldFilter(django_filters.CharFilter):
+    null_value = 'NULL'
+
+    def filter(self, qs, value):
+        if value != self.null_value:
+            return super(NullableCharFieldFilter, self).filter(qs, value)
+        qs = self.get_method(qs)(**{'{}__isnull'.format(self.name): True})
+        return qs.distinct() if self.distinct else qs
+
+
 class NullableModelMultipleChoiceField(forms.ModelMultipleChoiceField):
     """
     This field operates like a normal ModelMultipleChoiceField except that it allows for one additional choice which is