the queryset attribute of django REST api generic

问题:

I am trying to understand the django rest framework generic API views, the documentation tells me that while overriding methods of the generic views, I shouldn't be accessing the queryset attribute directly and instead access the get_queryset() function because apparently the queryset attribute is evaluated only once, what does the get_queryset() do differently? Does the queryset attribute ever get updated?

回答1:

To further expand, the source code will tell you the truth.

    assert self.queryset is not None, (
        "'%s' should either include a `queryset` attribute, "
        "or override the `get_queryset()` method."
        % self.__class__.__name__
    )

    queryset = self.queryset
    if isinstance(queryset, QuerySet):
        # Ensure queryset is re-evaluated on each request.
        queryset = queryset.all()
    return queryset

• First it checks queryset is defined
• Second it checks if the queryset specified is an instance of Django's Queryset class
• Third it re-evaluates (makes a database query) the queryset and sets the results
• Fourth it returns the results

The warning about using self.queryset directly is that results are cached when evaluated so further references to this value will not be up to date as opposed of using self.get_queryset().

回答2:

for simple views, the queryset attribute would quickly get your started. But in real life, normally, we have permissions on models, for example, the default queryset for a user would be filtered queryset based on request.user. The get_queryset method would become

def get_queryset(self):
    return self.model.objects.filter(user=self.request.user)

the above get_queryset method is just an example present real-life API design.