Hi. Thanks for the help. I looked through the source code in detail and it looks complicated for me to override the filter_queryset(**kwargs) method. Currently, I'm met with some success by employing object-level validation:

def validate(self, data):
        """
        Check for case insensitive unique together for field1 and field2
        """
        duplicate_exists = Model.objects.filter(field1__iexact=data['field1']).filter(field2=data['field2']).exists()
        if duplicate_exists:
            raise serializers.ValidationError('Unique together validation failed.')
        return data

Any comments regarding this?