Serialize a queryset.

def serialize(self, queryset, **options):
        """
        Serialize a queryset.
        """
        self.options = options

        self.stream = options.pop("stream", six.StringIO())
        self.selected_fields = options.pop("fields", None)
        self.use_natural_foreign_keys = options.pop('use_natural_foreign_keys', False)
        self.use_natural_primary_keys = options.pop('use_natural_primary_keys', False)
        progress_bar = self.progress_class(
            options.pop('progress_output', None), options.pop('object_count', 0)
        )

        self.start_serialization()
        self.first = True
        for count, obj in enumerate(queryset, start=1):
            self.start_object(obj)
            # Use the concrete parent class' _meta instead of the object's _meta
            # This is to avoid local_fields problems for proxy models. Refs #17717.
            concrete_model = obj._meta.concrete_model
            for field in self.get_local_fields(concrete_model):
                if field.serialize:
                    if field.remote_field is None:
                        if self.selected_fields is None or field.attname in self.selected_fields:
                            self.handle_field(obj, field)
                    else:
                        if self.selected_fields is None or field.attname[:-3] in self.selected_fields:
                            self.handle_fk_field(obj, field)
            for field in self.get_local_m2m_fields(concrete_model):
                if field.serialize:
                    if self.selected_fields is None or field.attname in self.selected_fields:
                        self.handle_m2m_field(obj, field)
            self.end_object(obj)
            progress_bar.update(count)
            if self.first:
                self.first = False
        self.end_serialization()
        return self.getvalue()