Fix person sorting

1. Same fix as DemocracyClub/WhoCanIVoteFor#1131
2. `sort_name` is NOT NULL so `Coalesce` always returned the sort name
3. Add `NullIfBlank` function to force sort name to return NULL

ynr/apps/elections/api/next/api_views.py

@@ -1,5 +1,6 @@
 from typing import OrderedDict
 from django.db.models import Prefetch
+from django.db.models.functions import Coalesce
 from django.utils.decorators import method_decorator
 from django.views.decorators.cache import cache_page
 from drf_yasg import openapi
@@ -16,7 +17,7 @@
 from elections.models import Election
 from official_documents.models import OfficialDocument
 from popolo.models import Membership
-from utils.db import LastWord
+from utils.db import LastWord, NullIfBlank
 
 
 class ElectionViewSet(viewsets.ReadOnlyModelViewSet):
@@ -46,12 +47,16 @@ class BallotViewSet(viewsets.ReadOnlyModelViewSet):
                 queryset=Membership.objects.all()
                 .select_related("result", "person", "party")
                 .annotate(last_name=LastWord("person__name"))
+                .annotate(
+                    name_for_ordering=Coalesce(
+                        NullIfBlank("person__sort_name"), "last_name"
+                    )
+                )
                 .order_by(
                     "-elected",
                     "-result__num_ballots",
                     "party_list_position",
-                    "person__sort_name",
-                    "last_name",
+                    "name_for_ordering",
                 ),
             ),
             Prefetch(

ynr/apps/popolo/querysets.py

@@ -2,8 +2,9 @@
 
 from django.db import models
 from django.db.models import Q
+from django.db.models.functions import Coalesce
 
-from utils.db import LastWord
+from utils.db import LastWord, NullIfBlank
 
 __author__ = "guglielmo"
 
@@ -96,10 +97,15 @@ def memberships_for_ballot(
         if ballot.election.party_lists_in_use:
             order_by += ["party__name", "party_list_position"]
         else:
-            order_by += ["person__sort_name", "last_name"]
+            order_by += ["name_for_ordering", "person__name"]
         qs = self.filter(ballot=ballot)
 
         qs = qs.annotate(last_name=LastWord("person__name"))
+        qs = qs.annotate(
+            name_for_ordering=Coalesce(
+                NullIfBlank("person__sort_name"), "last_name"
+            )
+        )
         qs = qs.order_by(*order_by)
         qs = qs.select_related("person", "person__image", "party", "result")
         if ballot.is_welsh_run:

ynr/apps/uk_results/forms.py

@@ -3,12 +3,13 @@
 from django import forms
 from django.core.exceptions import ValidationError
 from django.db import transaction
+from django.db.models.functions import Coalesce
 
 from candidates.models import LoggedAction
 from candidates.models.db import ActionType
 from candidates.views.version_data import get_client_ip
 from uk_results.helpers import RecordBallotResultsHelper
-from utils.db import LastWord
+from utils.db import LastWord, NullIfBlank
 
 from .models import CandidateResult, ResultSet
 
@@ -52,8 +53,13 @@ def __init__(self, ballot, *args, **kwargs):
         fields = OrderedDict()
         memberships = (
             ballot.membership_set.all()
-            .annotate(sorted_name=LastWord("person__name"))
-            .order_by("sorted_name")
+            .annotate(last_name=LastWord("person__name"))
+            .annotate(
+                name_for_ordering=Coalesce(
+                    NullIfBlank("person__sort_name"), "last_name"
+                )
+            )
+            .order_by("name_for_ordering")
         )
 
         for membership in memberships:

ynr/apps/utils/db.py

@@ -8,9 +8,7 @@ class LastWord(Transform):
 
     function = "LastWord"
     template = """
-    (regexp_split_to_array(%(field)s, ' '))[
-      array_upper(regexp_split_to_array(%(field)s, ' '), 1)
-    ]
+    regexp_replace(%(field)s, '^.* ', '')
     """
 
     def __init__(self, column, output_field=None):
@@ -20,6 +18,10 @@ def as_postgresql(self, compiler, connection):
         return self.as_sql(compiler, connection)
 
 
+class NullIfBlank(Func):
+    template = "NULLIF(%(expressions)s, '')"
+
+
 class Levenshtein(Func):
     """
     Uses postgres fuzzystrmatch to determine similarity between