cache_url doesn't handle backend properly.

[RemiDesgrange]

I have no idea if it's bug or a feature:

let's say I have 2 env var:

DEFAULT_COMPONENT_URL=dummycache://
DEFAULT_COMPONENT_BACKEND=dumy

in settings.py

import environ
from pathlib import Path

BASE_DIR = Path(environ.Path())
env = environ.FileAwareEnv(
    interpolate=True,
)
environ.Env.read_env(BASE_DIR / ".env")
CACHES = {
    "default": env.cache_url(
        "DEFAULT_CACHE_URL",
        f"redis://redis:6379/1",
        backend=env.str("DEFAULT_CACHE_BACKEND", "django_redis.cache.RedisCache"),
    )
}

the backend is set here

django-environ/environ/environ.py

Line 629 in 8874288

'BACKEND': cls.CACHE_SCHEMES[url.scheme],

to django.core.cache.backends.dummy.DummyCache.

But the backendkey is reset to the default value 44 lines later here

django-environ/environ/environ.py

Lines 673 to 674 in 8874288

	if backend:
	config['BACKEND'] = backend

no idea if this is intentional or not. I the fix is only removing the if backend line I'll be happy to submit a PR.

[sergeyklay]

Hi @RemiDesgrange,

Thank you for bringing this issue to our attention. To better understand the problem and evaluate your proposed solution, could you please provide a test case that reproduces the issue? A test that highlights the current problems and needs would be particularly helpful.

[RemiDesgrange]

Ok, in what form this solution should be provided ? The settings.py I gave can be executed in a shell (without even django). Do you need a test case with pytest etc... ?

Thx.

[sergeyklay]

Ok, in what form this solution should be provided ? The settings.py I gave can be executed in a shell (without even django). Do you need a test case with pytest etc... ?

Thx.

Providing a unit test would be ideal

[fdemmer]

@RemiDesgrange

in your example you mention DEFAULT_COMPONENT_URL. is that a typo? should it mean DEFAULT_CACHE_URL?

no idea if this is intentional or not. I the fix is only removing the if backend line I'll be happy to submit a PR.

i am guessing it is intentional, although there is no documentation or testcase for it.

the backend kwarg should override the backend determined via the "scheme" and can be used to set a specific cache backend implementation, e.g.:

# use 3rd party django-redis backend instead of built-in
env.cache_url("redis://redis:6379/1", backend="django_redis.cache.RedisCache")

A few other shortcuts support the same mechanism, like db(engine=...), email(backend=...) or search_url(engine=...).

edit: correction, here's a test:

django-environ/tests/test_cache.py

Line 173 in df301b6

def test_custom_backend():

/cc @sergeyklay looks like this is properly working and tested; may need docs.

[RemiDesgrange]

Sorry DEFAULT_CACHE_URL it is. DEFAULT_COMPONENT_URL is indeed a typo.

Thanks for the clarification.