Remove the nb_{yes,no} fields

These fields duplicate information that is already present in the Answer
table. I guess they exist(ed) as an optimisation to avoid recomputing
the number of positive and negative answers per proposition each time
the list page is loaded. Given the small number of propositions we have
in practice and the extra housekeeping required to keep these fields up
to date, I consider simplicity matters more here.

propositions/migrations/0005_remove_nb_yes_no_fields.py

@@ -0,0 +1,24 @@
+# Generated by Django 2.2.9 on 2020-01-05 15:26
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("propositions", "0004_prop_renaming_and_cleaning"),
+    ]
+
+    operations = [
+        migrations.RemoveField(model_name="proposition", name="nb_no",),
+        migrations.RemoveField(model_name="proposition", name="nb_yes",),
+        migrations.AlterField(
+            model_name="answer",
+            name="proposition",
+            field=models.ForeignKey(
+                on_delete=django.db.models.deletion.CASCADE,
+                to="propositions.Proposition",
+            ),
+        ),
+    ]

propositions/models.py

@@ -12,8 +12,6 @@ class Proposition(models.Model):
         ErnestoUser, on_delete=models.CASCADE, verbose_name="Proposé par"
     )
     link = models.URLField(blank=True)
-    nb_yes = models.IntegerField(default=0, verbose_name="nombre de réponses oui")
-    nb_no = models.IntegerField(default=0, verbose_name="nombre de réponses non")
 
     def __str__(self):
         return self.name
@@ -27,10 +25,7 @@ class Answer(models.Model):
     YES = "oui"
     NO = "non"
 
-    REP_CHOICES = [
-        (YES, "Oui"),
-        (NO, "Non")
-    ]
+    REP_CHOICES = [(YES, "Oui"), (NO, "Non")]
 
     proposition = models.ForeignKey(Proposition, on_delete=models.CASCADE)
     user = models.ForeignKey(User, on_delete=models.CASCADE)

propositions/tests.py

@@ -44,8 +44,6 @@ class PropositionCreateTest(TestCase):
         self.assertEqual(proposition.artist, "bar")
         self.assertEqual(proposition.link, "http://example.com")
         self.assertEqual(proposition.user, user.profile)
-        self.assertEqual(proposition.nb_yes, 0)
-        self.assertEqual(proposition.nb_no, 0)
 
 
 class PropositionListTest(TestCase):
@@ -99,11 +97,13 @@ class ReponseTest(TestCase):
         # Oui
         client.get(reverse("propositions:oui", args=(self.prop.id,)))
         self.prop.refresh_from_db()
-        self.assertEqual(self.prop.nb_yes, 1)
-        self.assertEqual(self.prop.nb_no, 0)
+        self.assertEqual(
+            list(self.prop.answer_set.values_list("answer", flat=True)), [Answer.YES],
+        )
 
         # Oui
         client.get(reverse("propositions:non", args=(self.prop.id,)))
         self.prop.refresh_from_db()
-        self.assertEqual(self.prop.nb_yes, 0)
-        self.assertEqual(self.prop.nb_no, 1)
+        self.assertEqual(
+            list(self.prop.answer_set.values_list("answer", flat=True)), [Answer.NO]
+        )

propositions/urls.py

@@ -8,7 +8,7 @@ app_name = "propositions"
 urlpatterns = [
     path("", views.PropositionList.as_view(), name="list"),
     path("new", views.PropositionCreate.as_view(), name="create"),
-    path("<int:id>/oui", views.answer, {"rep": "oui"}, name=Answer.YES),
-    path("<int:id>/non", views.answer, {"rep": "non"}, name=Answer.NO),
+    path("<int:id>/oui", views.answer, {"ans": "oui"}, name=Answer.YES),
+    path("<int:id>/non", views.answer, {"ans": "non"}, name=Answer.NO),
     path("<int:pk>/supprimer", PropDelete.as_view(), name="delete"),
 ]

propositions/views.py

@@ -2,6 +2,7 @@ from django.shortcuts import redirect, get_object_or_404
 from django.urls import reverse_lazy
 from django.contrib.auth.decorators import login_required
 from django.contrib.auth.mixins import LoginRequiredMixin
+from django.db.models import Count, Q
 from django.views.generic import CreateView, DeleteView, ListView
 from django.utils.decorators import method_decorator
 from django.http import HttpResponseRedirect
@@ -26,7 +27,14 @@ class PropositionList(LoginRequiredMixin, ListView):
     template_name = "propositions/liste.html"
     context_object_name = "propositions"
     model = Proposition
-    ordering = ["-nb_yes", "nb_no", "name"]
+
+    def get_queryset(self):
+        return (
+            Proposition.objects
+            .annotate(nb_yes=Count("answer", filter=Q(answer__answer=Answer.YES)))
+            .annotate(nb_no=Count("answer", filter=Q(answer__answer=Answer.NO)))
+            .order_by("-nb_yes", "nb_no", "name")
+        )
 
 
 class PropDelete(DeleteView):
@@ -50,24 +58,9 @@ class PropDelete(DeleteView):
 
 
 @login_required
-def answer(request, id, rep):
+def answer(request, id, ans):
     proposition = get_object_or_404(Proposition, id=id)
     user = request.user
-
-    old_answer = Answer.objects.filter(proposition=proposition, user=user)
-    if old_answer.exists():
-        old_answer = old_answer.get()
-        if old_answer.answer == Answer.YES:
-            proposition.nb_yes -= 1
-        else:
-            proposition.nb_no -= 1
-        old_answer.delete()
-
-    Answer.objects.create(proposition=proposition, user=user, answer=rep)
-    if rep == Answer.YES:
-        proposition.nb_yes += 1
-    else:
-        proposition.nb_no += 1
-    proposition.save()
-
+    Answer.objects.filter(proposition=proposition, user=user).delete()
+    Answer.objects.create(proposition=proposition, user=user, answer=ans)
     return redirect("propositions:list")