django-annotated-property 0.1.0

Decorator for Django model properties that checks if an annotation exists on the instance.

Django Annotated Property

Decorator for Django model properties that returns annotated values when available, avoiding database queries (f.e. O(N) vs O(1) for N items).

If a queryset includes annotated_<property>, the decorator uses it instead of calling the original method.

Example

from django.db import models
from django_annotated_property.annotated_property import annotated_property

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField(max_digits=8, decimal_places=2)

class OrderItem(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    quantity = models.PositiveIntegerField()

    @annotated_property
    def total_price(self):
        return self.product.price * self.quantity

now you can use the total_price property in your views or templates:

items = (
    OrderItem.objects
    .annotate(annotated_total_price=models.F('product__price') * models.F('quantity'))
)
for item in items:
    print(item.total_price)  # returns annotated_total_price instead of the original method

TODO

• Add tests