CODEWITHSUNDEEP
djangodjango-models
alias51
alias51

Reputation: 8608

How does django handle cached_property invalidation in a request/response cycle?

Say I have a model with a cached property:

class MyModel(models.Model):
    name = fields.Charfield()

    @cached_property
    def count_friends(self):
        return self.friends_set.count()

Django states that:

The cached result will persist as long as the instance does, so if the instance is passed around and the function subsequently invoked, the cached result will be returned.

How does this means cached_property works in the request/response cycle? For example, if I only use object.count_friends in a template, will it be refreshed each time the view is called (assuming browser cache is cleared!)?

Have I understood this correctly? E.g. each time I make a call to the DB, I assume it's refreshed?

In what practical circumstances would it not be refreshed?

Upvotes: 1

Views: 832

Answers (1)

AKX
AKX

Reputation: 169032

@cached_propertys are cached per-instance. The request-response cycle has no bearing on this (unless you stow away models as e.g. global variables which you shouldn't do or in the Django cache, ...)

def my_view(request):
    m = MyModel.objects.get(id=42)
    x = m.count_friends  # causes a DB access
    x = m.count_friends  # does not cause a DB access
    m = MyModel.objects.get(id=42)
    x = m.count_friends  # causes a DB access
    x = m.count_friends  # does not cause a DB access

Upvotes: 1

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