Validate the user if the review for the book already exists or not using DRF

Validate the user if the review for the book already exists or not in DRF

ReviewsSerializer

class ReviewsSerializer(serializers.ModelSerializer):
      
        
        class Meta:
            fields = ('id', 'user', 'text', 'created_at','book','rating')
            model = Reviews

        def validate_user(self, user):


            data = Reviews.objects.filter(user=user)
            print(data)
            request = self.context['request']
            c =  request.data

            # if Reviews.objects.filter(book=request.user).exists():
            #     print("ex")
            # else:
            #  print("no")

            #g = Reviews.objects.get(book=request.user)

            #book= get_object_or_404(book, pk=request.c)

            book_id = self.instance
               #book_id = self.context['request'].get('book_id')
            book_id = self.instance.id

            ca = Reviews.objects.filter(company=book_id, user=request.user).exists()

            try:
               pass
               #g = Reviews.objects.filter(book__user__reviews=request)
               #g = Reviews.objects.filter(book=request.user).exists()
               # return user
            except:
                raise serializers.ValidationError(("user already submitted a review for that book"))

            return user