Fewer db requests with AccountNegative handling.

- AccountNegative use new AccountNegativeManager which select_related
  account, cofprofile and user for instances accessed via
  AccountNegative.objects.
- Compute sum of negatives with python instead of an SQL statement
  (since we already got the data with a previous query).
- Fix bug on account property `real_balance` (happened if
  an account has a relative AccountNegative instance but balance_offset
  to NULL).

- More compliant to PEP8

kfet/models.py

@@ -96,7 +96,8 @@ class Account(models.Model):
     # Propriétés supplémentaires
     @property
     def real_balance(self):
-        if (hasattr(self, 'negative')):
+        if (hasattr(self, 'negative') and
+                self.negative.balance_offset is not None):
             return self.balance - self.negative.balance_offset
         return self.balance
 
@@ -229,27 +230,43 @@ class Account(models.Model):
         def __init__(self, trigramme):
             self.trigramme = trigramme
 
+
+class AccountNegativeManager(models.Manager):
+    """Manager for AccountNegative model."""
+
+    def get_queryset(self):
+        return (
+            super().get_queryset()
+            .select_related('account__cofprofile__user')
+        )
+
+
 class AccountNegative(models.Model):
+    objects = AccountNegativeManager()
+
     account = models.OneToOneField(
-        Account, on_delete = models.PROTECT,
-        related_name = "negative")
-    start = models.DateTimeField(
-        blank = True, null = True, default = None)
+        Account, on_delete=models.PROTECT,
+        related_name="negative",
+    )
+    start = models.DateTimeField(blank=True, null=True, default=None)
     balance_offset = models.DecimalField(
         "décalage de balance",
         help_text="Montant non compris dans l'autorisation de négatif",
-        max_digits = 6, decimal_places = 2,
-        blank = True, null = True, default = None)
+        max_digits=6, decimal_places=2,
+        blank=True, null=True, default=None,
+    )
     authz_overdraft_amount = models.DecimalField(
         "négatif autorisé",
-        max_digits = 6, decimal_places = 2,
-        blank = True, null = True, default = None)
+        max_digits=6, decimal_places=2,
+        blank=True, null=True, default=None,
+    )
     authz_overdraft_until = models.DateTimeField(
         "expiration du négatif",
-        blank = True, null = True, default = None)
-    comment = models.CharField("commentaire", max_length = 255, blank = True)
+        blank=True, null=True, default=None,
+    )
+    comment = models.CharField("commentaire", max_length=255, blank=True)
+
 
-@python_2_unicode_compatible
 class Checkout(models.Model):
     created_by = models.ForeignKey(
         Account, on_delete = models.PROTECT,

kfet/views.py

@@ -540,10 +540,13 @@ class AccountGroupUpdate(UpdateView):
     success_message = 'Groupe modifié : %(name)s'
     success_url = reverse_lazy('kfet.account.group')
 
+
 class AccountNegativeList(ListView):
-    queryset = (AccountNegative.objects
+    queryset = (
+        AccountNegative.objects
         .select_related('account', 'account__cofprofile__user')
-        .exclude(account__trigramme='#13'))
+        .exclude(account__trigramme='#13')
+    )
     template_name = 'kfet/account_negative.html'
     context_object_name = 'negatives'
 
@@ -553,14 +556,8 @@ class AccountNegativeList(ListView):
             'overdraft_amount': Settings.OVERDRAFT_AMOUNT(),
             'overdraft_duration': Settings.OVERDRAFT_DURATION(),
         }
-        negs_sum = (AccountNegative.objects
-            .exclude(account__trigramme='#13')
-            .aggregate(
-                bal    = Coalesce(Sum('account__balance'),0),
-                offset = Coalesce(Sum('balance_offset'),0),
-            )
-        )
-        context['negatives_sum'] = negs_sum['bal'] - negs_sum['offset']
+        real_balances = (neg.account.real_balance for neg in self.object_list)
+        context['negatives_sum'] = sum(real_balances)
         return context
 
 # -----