Introduce custom OrderingFilter to control NULLs & include tiebreaker

netbox/netbox/api/filter_backends.py

@@ -0,0 +1,34 @@
+from django.db.models import F
+from rest_framework import filters
+
+__all__ = (
+    'OrderingFilter',
+)
+
+
+class OrderingFilter(filters.OrderingFilter):
+    """
+    Extends DRF's OrderingFilter to sort null values last irrespective of the sort direction, and to
+    append a stable tiebreaker so that paginating through tied rows cannot skip or repeat them.
+    (PostgreSQL sorts nulls first when ordering descending, which pushes rows with no value to the
+    top of a descending sort.)
+
+    A viewset may map a field name to a query expression via `ordering_expressions` to order by
+    something other than the named column; this is used where the value presented to the user is
+    computed rather than stored.
+    """
+    def filter_queryset(self, request, queryset, view):
+        if not (ordering := self.get_ordering(request, queryset, view)):
+            return queryset
+
+        expressions = getattr(view, 'ordering_expressions', {})
+        terms = []
+        for term in ordering:
+            if descending := term.startswith('-'):
+                term = term[1:]
+            expression = expressions[term] if term in expressions else F(term)
+            terms.append(
+                expression.desc(nulls_last=True) if descending else expression.asc(nulls_last=True)
+            )
+
+        return queryset.order_by(*terms, 'pk')