paper 0.1.0

Keep generated fields in cache for your Django models.

Keep generated fields in cache for your Django models.

Usage

Just like the @property decorator, you just need to use the @paper decorator, that will transform a method of your class into a cached property.

class ModelA(models.Model):
    name = models.TextField()

    @paper(1, [
        ('testpaper.ModelB', lambda i: ModelA.objects.filter(children=i)),
    ])
    def count(self):
        return ModelA.objects\
            .filter(pk=self.pk)\
            .annotate(count=Coalesce(Sum('children__count'), 0))\
            .values_list('count', flat=True)[0]


class ModelB(models.Model):
    parent = models.ForeignKey('ModelA', related_name='children')
    count = models.IntegerField()

@paper takes 2 arguments:

• The method’s version number, in case you want to change the format of what is returned. By example, imagine you’re returning a complex denormalized data structure. If at some point you want to add some data in it, you can simply bump the version number and it will invalidate the caches automatically.

• A list of model/lister couples. - The model is either a model class, either an ‘app.Model’ string - The lister takes a single argument which is an instance of the updated model (here a ModelB objet) and returns a list of affected objects to invalidate (here a queryset of ModelA objects).

The value will be cached using Django’s default cache. Please note that this requires the cache to be shared across all your web worker instances, otherwise invalidation won’t have any the intended effect.

Invalidation is based on Django signals, so it requires save() or delete() to be called in order to work correctly. Bulk/SQL operations won’t be detected automatically.

Licence

This software is licenced by ActivKonnect under the terms of the WTFPL.