class PrefetchedFieldsSerializerMixin:
    "Serializer mixin that helps to avoid N+1 issue."

    @staticmethod
    def get_fields_to_be_prefetched(request):
        """Basic method to be overridden.

        Returns fields should to be prefetched
        before serialization to avoid N+1 issue.

        Args:
            request: django request object

        Expected return:
            fields: List[Union[str, Prefetch]]
        """

        raise NotImplementedError

    def get_nested_fields_to_be_prefetched(
        self, parent_field_prefix, request
    ) -> List[Union[str, Prefetch]]:
        """Doing the same as get_fields_to_be_prefetched
        method, but also adds parent field as prefix.

        Should be used to avoid N+1 issue in case of
        nested serialization of related field.
        """

        prefetch_fields = []

        for nested_field in self.get_fields_to_be_prefetched(request):

            if isinstance(nested_field, str):
                nested_field = f"{parent_field_prefix}__{nested_field}"

            elif isinstance(nested_field, Prefetch):
                nested_field.add_prefix(parent_field_prefix)

            else:
                message = f"""
                Type {type(nested_field)} cannot be used in prefetch_related
                method. Use str or Prefetch object instead.
                """

                raise TypeError(message)

            prefetch_fields.append(nested_field)

        return prefetch_fields

    def to_representation(self, instance):
        return super().to_representation(self._prefetch_fields(instance))

    def _prefetch_fields(self, instance):
        """Prefetches fields in case ther are't prefetched yet.

        This method solves errors when serializer includes dynamic
        fields generated by Prefetch() objects if they are not prefetched yet."""

        if not hasattr(instance, "_prefetched_objects_cache"):
            prefetch_fields = self.get_fields_to_be_prefetched(
                self.context.get("request")
            )
            prefetch_related_objects([instance], *prefetch_fields)
        return instance