Fix #116: Remove default SOA in Extension & Force reversion context

- The default for extension SOA is now None, else a new SOA named `SOA
to edit` was created when adding a new extension (because of the
get_or_create() )
- The mixins are now inside a reversion context else sometimes the
reversion context was not set and re2o would crash on the set_comment

machines/models.py

@@ -541,8 +541,7 @@ class Extension(RevMixin, AclMixin, models.Model):
     )
     soa = models.ForeignKey(
         'SOA',
-        on_delete=models.CASCADE,
-        default=SOA.new_default_soa
+        on_delete=models.CASCADE
     )
 
     class Meta:

re2o/mixins.py

@@ -24,6 +24,7 @@ A set of mixins used all over the project to avoid duplicating code
 """
 
 from reversion import revisions as reversion
+from django.db import transaction
 
 
 class RevMixin(object):
@@ -33,11 +34,14 @@ class RevMixin(object):
     def save(self, *args, **kwargs):
         """ Creates a version of this object and save it to database """
         if self.pk is None:
+            with transaction.atomic(), reversion.create_revision():
                 reversion.set_comment("Création")
                 return super(RevMixin, self).save(*args, **kwargs)
+        return super(RevMixin, self).save(*args, **kwargs)
 
     def delete(self, *args, **kwargs):
         """ Creates a version of this object and delete it from database """
+        with transaction.atomic(), reversion.create_revision():
             reversion.set_comment("Suppresion")
             return super(RevMixin, self).delete(*args, **kwargs)