Refactor Assignment model to enforce single rota assignment per worker and update related view logic to prevent multiple assignments

djangorota/rota/management/commands/find_multiple_assignments.py

@@ -0,0 +1,16 @@
+from django.core.management.base import BaseCommand
+from django.db.models import Count
+
+from rota.models import Worker
+
+
+class Command(BaseCommand):
+    help = "List workers assigned to more than one rota (useful before migrating to OneToOne Assignment)"
+
+    def handle(self, *args, **options):
+        qs = Worker.objects.annotate(num_rotas=Count('rotas')).filter(num_rotas__gt=1)
+        if not qs.exists():
+            self.stdout.write(self.style.SUCCESS('No workers assigned to more than one rota.'))
+            return
+        for w in qs:
+            self.stdout.write(f"Worker id={w.id} name={w.name!r} assigned_rotas={w.num_rotas}")