up and down votes

apps/core/test_app.py

+from core.apps import CoreConfig
+
+
+def test_init():
+    assert CoreConfig.name == 'core'

apps/rp/models/votes.py

+from django.db import models
+from django.db.models import Sum, F
+from django.contrib.contenttypes.fields import GenericForeignKey
+from django.contrib.contenttypes.fields import GenericRelation
+from django.contrib.contenttypes.models import ContentType
+from django.contrib.auth.models import User
+
+
+class UnDVotes(models.Model):
+    """
+    Up and down vote model
+    """
+    user = models.ForeignKey(
+        User,
+        on_delete=models.CASCADE,
+    )
+
+    #: Upvote, True for upvote, false for downvote
+    score = models.IntegerField(default=True)
+    # Django generic relation
+    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
+    object_id = models.PositiveIntegerField()
+    #: The Voted object
+    content_object = GenericForeignKey("content_type", "object_id")
+
+    def __str__(self):
+        return "{}:{}:{}".format(self.user, self.content_object, self.score)
+
+
+class UnDVotedMixin(models.Model):
+    """
+    A mixin to attach to a model that has up and down votes
+    """
+    #: Votes
+    und_votes = GenericRelation(UnDVotes)
+    #: Score of the model
+    und_score = models.IntegerField(default=0)
+
+    def upvote(self, user):
+        diff_score = 0
+        try:
+            # Already voted content
+            vote = self.und_votes.get(user=user)
+            if vote.score == 1:
+                # Cancel previous upvote
+                vote.delete()
+                diff_score = -1
+            else:
+                # Previously downvoted
+                vote.score = 1
+                vote.save()
+                diff_score = 2
+        except:
+            vote = UnDVotes(content_object=self, user=user, score=1)
+            vote.save()
+            diff_score = 1
+
+        self.__class__.objects.filter(id=self.id).update(
+            und_score=F("und_score") + diff_score)
+
+    def downvote(self, user):
+        diff_score = 0
+        try:
+            # Already voted content
+            vote = self.und_votes.get(user=user)
+            if vote.score == -1:
+                # Cancel previous downvote
+                vote.delete()
+                diff_score = 1
+            else:
+                # Previously upvoted
+                vote.score = -1
+                vote.save()
+                diff_score = -2
+        except:
+            vote = UnDVotes(content_object=self, user=user, score=-1)
+            vote.save()
+            diff_score = -1
+
+        # Update self score, use update and filter to avoid triggering signals
+        self.__class__.objects.filter(id=self.id).update(
+            und_score=F("und_score") + diff_score)
+
+    def update_und_score(self):
+        """Reset score to the correct count (should not be necessary)"""
+        score = self.und_votes.aggregate(Sum("score"))["score__sum"] or 0
+        # Update self score, use update and filter to avoid triggering signals
+        self.__class__.objects.filter(id=self.id).update(und_score=score)
+
+    class Meta:
+        abstract = True