[Answered ]-Why do I get an old data set in one case after a GET request, and an up-to-date data set in the other

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QuerySets cache the value. That means that if you directly return self.queryset, it will run the query once, and store the values in memory.

If you add .all(), you make a copy of the QuerySet without the cache, and you thus force making a new query.

This is why a ListView by default has an implementation where it will return the queryset.all(). Indeed, if we look at the source code [GitHub], we see:

    def get_queryset(self):
        """
        Return the list of items for this view.
        The return value must be an iterable and may be an instance of
        `QuerySet` in which case `QuerySet` specific behavior will be enabled.
        """
        if self.queryset is not None:
            queryset = self.queryset
            if isinstance(queryset, QuerySet):
                queryset = queryset.all()
        elif self.model is not None:
            queryset = self.model._default_manager.all()
        else:
            raise ImproperlyConfigured(
                "%(cls)s is missing a QuerySet. Define "
                "%(cls)s.model, %(cls)s.queryset, or override "
                "%(cls)s.get_queryset()." % {
                    'cls': self.__class__.__name__
                }
            )
        ordering = self.get_ordering()
        if ordering:
            if isinstance(ordering, str):
                ordering = (ordering,)
            queryset = queryset.order_by(*ordering)

        return queryset
👤willeM_ Van Onsem

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