title: How to do filtering in Django Rest ModelViewset
body: <p>I have signup api. I'm adding signup details, data adding fine but I don't want to add same data multiple time.For example username="abc",  email= "abc@example.com",  phone_no="1234567890"  data already present in database but its adding same data again and again. I'm trying to avoid this. How to do that</p>
  
  <p>modes.py</p>
  
  <pre><code>class Signup(models.Model):
      email = models.EmailField(max_length=50, blank=True, null=True)
      phone_number = models.CharField(max_length=12, blank=True, null=True)
      username = models.CharField(max_length=300, blank=True, null=True)
      password = models.CharField(max_length=50, blank=True, null=True)
  </code></pre>
  
  <p>serializers.py</p>
  
  <pre><code>class SignupSerializer(serializers.ModelSerializer):
  
      class Meta:
          model = Signup
          fields = '__all__'
  </code></pre>
  
  <p>views.py</p>
  
  <pre><code>class SignupViews(viewsets.ModelViewSet):
      queryset = Signup.objects.all()
      serializer_class = SignupSerializer
  </code></pre>
  
  <p>urls.py</p>
  
  <pre><code>router = routers.DefaultRouter()
  router.register('api/signup', views.SignupViews)
  
  urlpatterns = [
      path('', include(router.urls))
  ]
  </code></pre>