title: Django rest framework ModelSerializer runs too slowly
body: <p>We want to provide an api for our django project,so we use drf (django rest framework).
  we use ModelSerializer which provides a shortcut that lets you automatically create a Serializer class with fields that correspond to the Model fields.
  Our problem is it runs very slowly.In other word,process of serialization takes about 40 second until retrieving the response.</p>
  
  <p>How we can reduce this delay?<br>
  VIEW</p>
  
  <pre><code>class MyObjViewSet(viewsets.ModelViewSet):
  
      pagination_class = LargeResultsSetPagination
  
      def get_queryset(self):
          queryset = MyObj.objects.all().order_by('time')
          return queryset
  
      serializer_class = MyObjSerializer
  </code></pre>
  
  <p>My Obj Model</p>
  
  <pre><code>class MyObj(models.Model):
      id = models.BigIntegerField(primary_key=True)
      time = models.DateTimeField()
      type = models.CharField(max_length=5)
      user = models.ForeignKey('User', related_name='myobj')
  </code></pre>
  
  <p>MyObj User Model</p>
  
  <pre><code>class User(models.Model):
      id = models.IntegerField(primary_key=True)
      username = models.CharField(max_length=80)
  </code></pre>
  
  <p>my Obj serializer</p>
  
  <pre><code>class MyObjSerializer(serializers.ModelSerializer):
  
      class Meta:
          model = MyObj
          fields = ('id', 'type', 'time', 'user')
  </code></pre>
  
  <p>My problem is when i want to retrieve list of my objs, its take about to 40 second!</p>