title: Serializer as Field is not visible in json
body: <h2>Model</h2>
  
  <p>class makitVerifications (models.Model):</p>
  
  <pre><code>Matter_fk = models.ForeignKey(Matter,on_delete=models.CASCADE , related_name = "makit_validate")
  
  user_fk =  models.ForeignKey('auth.User',on_delete=models.CASCADE ,  related_name = 'verification_by'   , )
  </code></pre>
  
  <h2>Serializer</h2>
  
  <p>class UserVerifyCountSerializer (serializers.ModelSerializer):</p>
  
  <pre><code># Tried makit_validate = makitSerializer (read_only = True)
  
  class Meta :
  
      model = makitVerifications
      fields = (  'user_fk', 'makit_validate', 'Matter_fk')
  </code></pre>
  
  <p>UserVerifyCountSerializer._declared_fields['makit_validate']= makitSerializer (read_only = True)</p>
  
  <h2>View</h2>
  
  <p>class UserVerfiyCountViewSet(generics.ListCreateAPIView):</p>
  
  <pre><code>serializer_class = UserVerifyCountSerializer
  
  def get_queryset(self):
  
      queryset = makitVerifications.objects.all()
  
      return queryset
  </code></pre>
  
  <h2>JSON</h2>
  
  <p>{
      "count": 2,
      "next": null,
      "previous": null,
      "results": [
          {
              "user_fk": 1,
              "Matter_fk": 1
          },
          {
              "user_fk": 1,
              "Matter_fk": 1
          }
      ]</p>
  
  <p>The field "makit_validate" which is expected as nested object is missing in the JSON .How can I get nested object  of the related model in json . </p>
  
  <p>I also tried an example from the docs but  the same field is missing  from JSON</p>
  
  <p>Also how to  omit/disable fields from the objected being nested in the above serializer class </p>
  
  <h2>Makie Serilazer</h2>
  
  <p>class makitSerializer(serializers.ModelSerializer):</p>
  
  <pre><code>kamaz = kamazSerializer(many=True,read_only=True)
  
  facilities = FacilitiesSerializer (many =True,read_only=True)
  
  class Meta :
  
      model = Makit
  
      fields = '__all__'
  
  ## Makit Model ##
  class Makit (models.Model): 
      pincode = models.IntegerField()
  
      area = models.CharField(max_length=200)
  
      street = models.CharField(max_length=200)
  
      landmark = models.CharField(max_length=100,blank=True , null = True)
  
      contact_no= models.BigIntegerField()
  </code></pre>