title: Update m2m,foreignkey field to model does not work in DRF
body: <p>Update to the following News model does not work in DRF.(
  address is not updated)
  The creation works fine.</p>
  
  <pre><code>class News (models.Model):
      id = models.AutoField(primary_key=True)
      title = models.CharField(max_length=20)
      text = models.TextField()
      group_address = models.ManyToManyField(Group, blank=True)
      user_address = models.ForeignKey(User, on_delete=models.CASCADE)
  
  
  class Group(models.Model):
      id = models.AutoField(primary_key=True)
      group_name = models.CharField(max_length=20)
  
  class User(models.Model):
      id = models.AutoField(primary_key=True)
      user_name = models.CharField(max_length=20)
  
  </code></pre>
  
  <pre><code>class NewsSerializerViewSet(viewsets.ModelViewSet):
      queryset = News.objects.all() 
      serializer_class = NewsSerializer 
  
  </code></pre>
  
  <pre><code>class NewsSerializer(serializers.ModelSerializer):
      class Meta:
          model = News
          fields = '__all__'
  </code></pre>