La cotis est onetone avec la facture

cotisations/migrations/0012_auto_20160704_0118.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('cotisations', '0011_auto_20160702_1911'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='cotisation',
+            name='facture',
+            field=models.OneToOneField(on_delete=django.db.models.deletion.PROTECT, to='cotisations.Facture'),
+        ),
+    ]

cotisations/models.py

@@ -40,7 +40,7 @@ class Paiement(models.Model):
         return self.moyen
 
 class Cotisation(models.Model):
-    facture = models.ForeignKey('Facture', on_delete=models.PROTECT)
+    facture = models.OneToOneField('Facture', on_delete=models.PROTECT)
     date_start = models.DateTimeField()
     date_end = models.DateTimeField()