How does @cached_property work in django?

Question

Django

I can't understand how @cached_property works in the model. It is necessary to display the count of records. I do it with the following method:

class Categorie(MPTTModel):
    class Meta:
        verbose_name = 'Категория'
        verbose_name_plural = 'Категории'

    def __str__(self):
        return self.name

    parent = TreeForeignKey('self', null=True, blank=True, related_name='children', db_index=True)
    name = models.CharField(unique=True, max_length=60)
    slug = models.SlugField(unique=True, max_length=80, default='')
    created_at = models.DateField(auto_now_add=True)

    class MPTTMeta:
        order_insertion_by = ['name']

    @cached_property
    def sites(self):
        return self.site_set.count()

But with every request to sites, there is a request to the database. In my understanding, it should work according to the following scheme: the first request to the database and all subsequent requests from the cache. After del sites again query the database. Help understand

Answer 1

You misunderstood cached _property, it is needed for lazy properties that will only be evaluated when called. There is an article on habr https://habrahabr.ru/post/159099/
And yes, this is not caching, but just lazy_load

Answer 2

If the project is already using redis, then cacheops is a good solution . can be configured to cache only count queries of a specific model.
It goes without saying that you should use it with caution, and only where you encounter loads, you should not cache everything in a row.