Fix content_object issue

-   Remove `content_object` attribute which can be `None` for deleted
    object
-   Use `snapshot` instead of `content_object` which would not be `None`
-   Stop defering `snapshot` to prevent N+1 problem

src/kawaz/apps/activities/mediator.py

@@ -16,8 +16,6 @@ class ActivityMediator(object):
     An ActivityMediator class which has responsivilities to controll automatic
     activity creation (with signal handling) or rendering.
     """
-    use_snapshot = False
-
     def _pre_delete_receiver(self, sender, instance, **kwargs):
         ct = ContentType.objects.get_for_model(instance)
         activity = Activity(content_type=ct,
@@ -26,9 +24,8 @@ def _pre_delete_receiver(self, sender, instance, **kwargs):
         # call user defined alternation code
         activity = self.alter(instance, activity, **kwargs)
         if activity:
-            # save current instance snapshot if 'use_snapshot'
-            if self.use_snapshot:
-                activity.snapshot = instance
+            # save current instance as a snapshot
+            activity.snapshot = instance
             activity.save()
 
     def _post_save_receiver(self, sender, instance, created, **kwargs):
@@ -39,19 +36,17 @@ def _post_save_receiver(self, sender, instance, created, **kwargs):
         # call user defined alternation code
         activity = self.alter(instance, activity, **kwargs)
         if activity:
-            # save current instance snapshot if 'use_snapshot'
-            if self.use_snapshot:
-                activity.snapshot = instance
+            # save current instance as a snapshot
+            activity.snapshot = instance
             activity.save()
 
     def _m2m_changed_receiver(self, sender, instance, **kwargs):
         # call user defined alternation code
         # user need to create activity instance
         activity = self.alter(instance, None, **kwargs)
         if activity:
-            # save current instance snapshot if 'use_snapshot'
-            if self.use_snapshot:
-                activity.snapshot = instance
+            # save current instance as a snapshot
+            activity.snapshot = instance
             activity.save()
 
     def connect(self, model):
@@ -109,7 +104,7 @@ def prepare_context(self, activity, context):
         """
         context.update({
             'activity': activity,
-            'object': activity.content_object
+            'object': activity.snapshot
         })
         return context
 

src/kawaz/apps/activities/models.py

@@ -14,10 +14,6 @@
 
 
 class ActivityManager(models.Manager):
-    def get_queryset(self):
-        # defer '_snapshot' column which only required during signal handling
-        # to accelerate database access
-        return super().get_queryset().defer('_snapshot')
 
     def latests(self):
         """
@@ -43,7 +39,6 @@ class Activity(models.Model):
 
     content_type = models.ForeignKey(ContentType)
     object_id = models.PositiveIntegerField('Object ID')
-    content_object = GenericForeignKey()
     _snapshot = models.BinaryField(default=None, null=True)
 
     created_at = models.DateTimeField(auto_now_add=True)

src/kawaz/apps/activities/registry.py

@@ -2,6 +2,7 @@
 """
 """
 __author__ = 'Alisue <lambdalisue@hashnote.net>'
+from django.contrib.contenttypes.models import ContentType
 from .mediator import ActivityMediator
 
 
@@ -38,7 +39,7 @@ def get(self, activity):
         """
         Get connected activity mediator of a model which the activity has.
         """
-        model = activity.content_object._meta.model
+        model = activity.content_type.model_class()
         return self._registry[model]
 
 

src/kawaz/apps/activities/tests/test_mediator.py

@@ -137,7 +137,7 @@ def test_prepare_context(self):
 
         context.update.assert_called_with({
             'activity': activity,
-            'object': activity.content_object,
+            'object': activity.snapshot,
         })
         self.assertEqual(c, context)
 

src/kawaz/apps/activities/tests/test_models.py

@@ -66,10 +66,10 @@ def test_attributes(self):
         activity = Activity()
         self.assertTrue(hasattr(activity, 'status'))
         self.assertTrue(hasattr(activity, 'remarks'))
-        self.assertTrue(hasattr(activity, 'content_object'))
         self.assertTrue(hasattr(activity, 'object_id'))
         self.assertTrue(hasattr(activity, 'created_at'))
         self.assertTrue(hasattr(activity, '_snapshot'))
+        self.assertTrue(hasattr(activity, 'snapshot'))
 
     def test_snapshot(self):
         model = self.models[0]

src/kawaz/apps/activities/tests/test_registry.py

@@ -37,6 +37,6 @@ def test_get(self):
         registry.register(model, mediator)
 
         activity = MagicMock()
-        activity.content_object._meta.model = model
+        activity.content_type.model_class = MagicMock(return_value=model)
 
         self.assertEqual(registry.get(activity), mediator)