title: Write only, read only fields in django rest framework
body: <p>I have models like this:</p>
  
  <pre><code>class ModelA(models.Model):
      name = models.CharField()
  
  
  class ModelB(models.Model):
      f1 = models.CharField()
      model_a = models.ForeignKey(ModelA)
  </code></pre>
  
  <p>Serializers:</p>
  
  <pre><code>class ASerializer(serializers.ModelSerializer):
      model_b_ids = serializers.CharField()
      class Meta:
          model = ModelA
          write_only_fields = ('model_b_ids',)
  </code></pre>
  
  <p>views:</p>
  
  <pre><code>class AView(CreateModelMixin, GenericViewSet):
  
      def perform_create(self, serializer): 
          model_b_ids = parse_somehow(serializer.validated_data["model_b_ids"])
          #do something...
  </code></pre>
  
  <p>The problem I am getting is the with the "model_b_ids"</p>
  
  <p>The user should submit it while sending post data.</p>
  
  <p>I use it in perform_create to link to related models. </p>
  
  <p>But thats not "real column" in ModelA so when I try to save it is raising exception.</p>
  
  <p>I tried to it pop from validated_data but then again getting error somewhere that cannot read model_b_ids from model. Any idea on using this kind of field correctly ?</p>