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django-cache-mock

Use in-process mocks to avoid setting up external caches for Django during development.

Django has a limited built-in django.core.cache.backends.locmem.LocMemCache, to help development, but Django do some magic to always give you a working connection.

I have some reasons to abuse Django cache this way:

  • Thread safety: Django spin one connection per thread to avoid issues with thread unsafe drivers.
  • Good defaults: Django run connections with good defaults.
  • Connection reuse: Django already have a pool running and in most cases it is better to use it.

Install

$ pip install django-cache-mock

Also, it is possible to install with the backends you want.

For mockcache, it installs mockcache3, a fork from original package because it doesn´t work for new versions of Python.

$ pip install django-cache-mock[mockcache]
$ pip install django-cache-mock[fakeredis]
$ pip install django-cache-mock[redislite]

How to use

In your Django settings you already have CACHES defined.

For memcached, it's something like that:

CACHES = {
    "default": {
        "BACKEND": "django.core.cache.backends.memcached.PyMemcacheCache",
        "LOCATION": os.getenv("MEMCACHED_HOSTS"),
        "OPTIONS": {
            "no_delay": True,
            "ignore_exc": True,
            "max_pool_size": 4,
            "use_pooling": True,
        },
    },
}

Just make a call to django_cache_mock.patch to replace with a mock backend.

The lib will patch only when cache LOCATION is not defined.

import django_cache_mock

if DEBUG:  # Apply it only in debug mode to be extra careful.
    django_cache_mock.patch(CACHES, "default", "mockcache")

This patch replace cache with a mocked one. For mockcache,

Custom cache options

The patch function accepts custom params. It can be used to override mock behaviours, like the db file redislite will use, defined by LOCATION:

django_cache_mock.patch(CACHES, "default", "redislite", {"LOCATION": "data/redis.db"})

Redis backends

Redis has several options to run. This lib implements fakeredis and redislite, with django.core.cache or django-redis.

By default, the lib try to maintain the same behavior of the original implementation. If config uses django-redis, when you set use backend fakeredis, it will use it as fakeredis[django-redis].

# Force to use django-redis. It is not necessary, the lib already try to use
# django-redis if cache uses `django_redis.cache.cache.RedisCache`.
django_cache_mock.patch(CACHES, "redis", "fakeredis[django-redis]")
django_cache_mock.patch(CACHES, "redis", "redislite[django-redis]")

How to access connections

To get Django memcached and redis clients from cache:

from django.core.cache import caches

def give_me_memcached():
    return caches["memcached"]._cache

# for django.core.cache.backends.redis
def give_me_primary_redis():
    return caches["redis"]._cache.get_client(write=True)

def give_me_secondary_redis():
    return caches["redis"]._cache.get_client()

# for django-redis
def give_me_primary_redis():
    return caches["redis"].client.get_client()

def give_me_secondary_redis():
    return caches["redis"].client.get_client(write=False)

# Yes, django and django-redis have different write flag defaults.