Django DBCache Fields

About

This library provides a decorator dbcache that caches the result of your Django Model methods in your database.

It adds a regular Field on your Model for each method that you decorate. This means you can use all ORM-functions like aggregation and migrations. You can use existing fields or let dbcache create the field for you.

You can also invalidate the cached value by creating a _dirty_ function or by indicating which other models affect the this cached value. By default, the cached value is only updated when the model is saved.

Installation

You can install django_dbcache_fields either via the Python Package Index (PyPI) or from source.

To install using pip:

$ pip install -U django_dbcache_fields

Usage

To use this with your project you need to follow these steps:

1. Install the django_dbcache_fields library:

   $ pip install django_dbcache_fields

2. Add django_dbcache_fields to INSTALLED_APPS in your Django project's settings.py:

   INSTALLED_APPS = (
       # ...,
       'django_dbcache_fields',
   )

   Note that there is no dash in the module name, only underscores.

3. All done. You can now decorate methods in your Model with @dbcache.

Example

Simple example to show what dbcache does:

from django.db import models
from django_dbcache_fields.decorators import dbcache

class Ingredient(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField(max_digits=4, decimal_places=2)

class Pizza(models.Model):
    name = models.CharField(max_length=100)
    ingredients = models.ManyToManyField(Ingredient)

    @dbcache(models.DecimalField(max_digits=6, decimal_places=2,
             blank=True, null=True), invalidated_by=['myapp.Ingredient'])
    def get_price(self):
        return self.ingredients.aggregate(total=Sum('price'))['total'] or Decimal()

Every call to get_price would normally perform a database query to calculate the total price of all ingredients. However, the dbcache decorator caused a new field to be added to the model: A DecimalField that can store the resulting value of the get_price function, so it doesn't need to perform the same query over and over again.