adding small clarification on nested serializiers via through models

docs/api-guide/relations.md

@@ -569,6 +569,65 @@ For more information see [the Django documentation on generic relations][generic
 
 ## ManyToManyFields with a Through Model
 
+Example, given the following models:
+
+    class Artist(models.Model):
+        name = models.CharField(max_length=180)
+    
+        def __str__(self):
+            return self.name
+    
+    
+    class Portfolio(models.Model):
+        user = models.ForeignKey(get_user_model(), on_delete=models.CASCADE)
+        name = models.CharField(max_length=180)
+        artists = models.ManyToManyField(Artist, through='Calification')
+    
+        def __str__(self):
+            return '{} - {}'.format(self.user, self.name)
+    
+    
+    class Calification(models.Model):
+        portfolio = models.ForeignKey(Portfolio, on_delete=models.CASCADE, related_name='califications')
+        artist = models.ForeignKey(Artist, on_delete=models.CASCADE)
+        rate = models.IntegerField(default=0)
+        added_at = models.DateTimeField(auto_now_add=True)
+    
+        def __str__(self):
+            return '{} - {} - {}'.format(self.portfolio, self.artist, self.rate)
+            
+We could serialize them as follows:
+
+    class ArtistSerializer(serializers.ModelSerializer):
+
+        class Meta:
+            model = Artist
+            fields = ('name', )
+    
+    
+    class CalificationSerializer(serializers.ModelSerializer):
+    
+        artist = ArtistSerializer()
+    
+        class Meta:
+            model = Calification
+            fields = ('artist', 'rate', 'added_at')
+    
+    
+    class PortfolioSerializer(serializers.ModelSerializer):
+    
+        artists = CalificationSerializer(many=True, source='califications')
+    
+        class Meta:
+            model = Portfolio
+            fields = ('id', 'name', 'user', 'artists', )
+            
+
+It's important to remember that it's easier if we set a ``related_name`` to the foreign_key we want to follow from the main model.
+If we don't set it we would have to set the attribute ``source`` of the nested serializer ``CalificationSerializer`` as
+
+    artists = CalificationSerializer(many=True, source='calification_set.all') 
+
 By default, relational fields that target a ``ManyToManyField`` with a
 ``through`` model specified are set to read-only.