Remove is_checkout field from Operation model

kfet/models.py

@@ -510,12 +510,14 @@ class Operation(models.Model):
     DEPOSIT  = 'deposit'
     WITHDRAW = 'withdraw'
     INITIAL = 'initial'
+    EDIT = 'edit'
 
     TYPE_ORDER_CHOICES = (
         (PURCHASE, 'Achat'),
         (DEPOSIT, 'Charge'),
         (WITHDRAW, 'Retrait'),
         (INITIAL, 'Initial'),
+        (EDIT, 'Édition'),
     )
 
     group = models.ForeignKey(
@@ -527,7 +529,6 @@ class Operation(models.Model):
     amount = models.DecimalField(
         max_digits = 6, decimal_places = 2,
         blank = True, default = 0)
-    is_checkout = models.BooleanField(default = True)
     # Optional
     article = models.ForeignKey(
         Article, on_delete = models.PROTECT,
@@ -549,6 +550,14 @@ class Operation(models.Model):
         max_digits = 6, decimal_places = 2,
         blank = True, null = True, default = None)
 
+    @property
+    def is_checkout(self):
+        return (self.type == DEPOSIT or
+                self.type == WITHDRAW or
+                (self.type == PURCHASE and self.group and
+                 self.group.on_acc.is_cash)
+                )
+
 class GlobalPermissions(models.Model):
     class Meta:
         managed = False