title: Django query does not update when database changes
body: <p>I have a weird problem, I think it comes from the cache between django and postgres but not so sure.</p>
  
  <p>I have multiple tables in database but the problem only happens with one of them. Let's say the SpeakingSession table. Everytime I make a change like add a new instance, edit an instance, the call api request does not return the change; the data is only updated when I restart the apache2 server.</p>
  
  <p>For example: I have 7 SpeakingSession records, then I add a new one. But the print command below returns 7.</p>
  
  <pre><code>class SpeakingSessionViewSet(viewsets.ModelViewSet):
  
      queryset = SpeakingSession.objects.all()
  
      def list(self, request):
          print(self.queryset.count())
          return super(SpeakingSessionViewSet, self).list(request)
  </code></pre>
  
  <p>So I restart the apache2 server, then it returns 8.</p>
  
  <p>Any idea how to fix this problem? Thank you very much!</p>
  
  <p>This is my model and my serializer:</p>
  
  <pre><code>class SpeakingSession(models.Model):
  
      sessionDefinition = models.ForeignKey('SessionDefinition', on_delete=models.CASCADE)
      startTime = models.TimeField()
      endTime = models.TimeField()
      participants = models.ManyToManyField('Profile', default=None, blank=True)
  
  class SpeakingSessionSerializer(serializers.ModelSerializer):
  
      class Meta:
          model = SpeakingSession
          fields = ('id', 'sessionDefinition', 'startTime', 'endTime', 'participants')
  </code></pre>