Adding check for subscription generator class on pre_save

newsletter/models.py

@@ -104,14 +104,14 @@ def get_templates(self, action):
     def get_subscription_generator(self):
         if self.subscription_generator_class:
             try:
-                class_data = self.subscription_generator_class.split(".")
-                module_name = ".".join(class_data[:-1]) if len(class_data) > 1 else ''
-                class_name = class_data[-1]
+                if "." not in self.subscription_generator_class:
+                    raise ModuleNotFoundError("missing module for subscription generator class")
+                module_name, class_name = self.subscription_generator_class.rsplit(".", 1)
                 module = importlib.import_module(module_name)
                 self.subscription_generator = getattr(module, class_name)()
                 return self.subscription_generator
             except (AttributeError, ModuleNotFoundError) as e:
-                logger.error("Could not load subscriber generator class '%s' - %s" % (self.subscription_generator_class, e))
+                logger.error(f"Could not load subscriber generator class '%s' - %s" % (self.subscription_generator_class, e))
                 raise e
         else:
             return None
@@ -154,6 +154,14 @@ def get_default(cls):
             return None
 
 
+def newsletter_presave(sender, instance, **kwargs):
+    if instance.subscription_generator_class:
+        instance.get_subscription_generator()
+
+
+models.signals.pre_save.connect(newsletter_presave, Newsletter)
+
+
 class Subscription(models.Model):
     user = models.ForeignKey(
         AUTH_USER_MODEL, blank=True, null=True, verbose_name=_('user'),