Add average rating for Song model.

savepointradio/api/serializers/radio.py

@@ -32,14 +32,16 @@ class GameSerializer(ModelSerializer):
 class BasicSongSerializer(ModelSerializer):
     class Meta:
         model = Song
-        fields = ('id', 'album', 'artists', 'game', 'title')
+        fields = ('id', 'album', 'artists', 'game', 'title', 'average_rating',
+                  'is_requestable')
 
 
 class FullSongSerializer(ModelSerializer):
     class Meta:
         model = Song
         fields = ('id', 'album', 'artists', 'published_date', 'game',
-                  'num_played', 'last_played', 'length', 'song_type', 'title')
+                  'num_played', 'last_played', 'length', 'song_type', 'title',
+                  'average_rating', 'is_requestable')
 
 
 class BasicSongRetrieveSerializer(BasicSongSerializer):

savepointradio/radio/models.py

@@ -1,4 +1,5 @@
 from datetime import timedelta
+from decimal import getcontext, Decimal, ROUND_UP
 
 from django.apps import apps
 from django.db import models
@@ -9,6 +10,10 @@ from core.behaviors import Disableable, Publishable, Timestampable
 from .managers import RadioManager, SongManager
 
 
+# Set decimal precision
+getcontext().prec = 16
+
+
 class Album(Disableable, Publishable, Timestampable, models.Model):
     """
     A model for a music album.
@@ -174,6 +179,17 @@ class Song(Disableable, Publishable, Timestampable, models.Model):
         return self.title
     full_title = property(_full_title)
 
+    def _average_rating(self):
+        """
+        Decimal number of the average rating of a song from 1 - 5.
+        """
+        ratings = self.rating_set.all()
+        if ratings:
+            avg = Decimal(ratings.aggregate(avg=models.Avg('value'))['avg'])
+            return avg.quantize(Decimal('.01'), rounding=ROUND_UP)
+        return None
+    average_rating = property(_average_rating)
+
     def get_time_until_requestable(self):
         """
         Length of time before a song can be requested again.