DATABASE_URL doesn't support custom backends when underscores in engine part

[fdobrovolny]

This works as expected:

>>> Env.db_url_config("custom.backend://user:password@example.com:5430/database")
{'NAME': 'database', 'USER': 'user', 'PASSWORD': 'password', 'HOST': 'example.com',
'PORT': 5430, 'ENGINE': 'custom.backend'}

Doesn't work:

>>> Env.db_url_config("some_custom.backend://user:password@example.com:5430/database")
/usr/local/lib/python3.7/site-packages/environ/environ.py:437: UserWarning: Engine 
not recognized from url:
{'NAME': 'ome_custom.backend://user:password@example.com:5430/database',
'USER': '', 'PASSWORD': '', 'HOST': '', 'PORT': '', 'ENGINE': ''}
  warnings.warn("Engine not recognized from url: {0}".format(config))
{}

>>> Env.db_url_config("custom.some_backend://user:password@example.com:5430/database")
/usr/local/lib/python3.7/site-packages/environ/environ.py:437: UserWarning: Engine
not recognized from url:
{'NAME': 'ustom.some_backend://user:password@example.com:5430/database', 
'USER': '', 'PASSWORD': '', 'HOST': '', 'PORT': '', 'ENGINE': ''}
  warnings.warn("Engine not recognized from url: {0}".format(config))
{}

[thiras]

I confirm the bug under;

• Python 3.6
• Django 2.1.5

This might be a Py compatibility issue. I think url parsing fails at environ.py L#375

[loicteixeira]

Same issue here.

In the meantime, I went around the issue by monkey patching the Env class to add my own database scheme this way:

from environ import Env

Env.DB_SCHEMES['mybackend'] = 'some_custom.backend'
Env.db_url_config('mybackend://user:password@example.com:5430/database')
# {'NAME': 'database', 'USER': 'user', 'PASSWORD': 'password', 'HOST': 'example.com', 'PORT': 5430, 'ENGINE': 'some_custom.backend'}

---

For what is worth, I tried to make it a bit cleaner by subclassing Env to make my own subclass like so:

from environ import Env

class ExtendedEnv(Env):
    DB_SCHEMES = {
        **Env.DB_SCHEMES,
        'mybackend': 'some_custom.backend',
    }

However it doesn't work since Env.db_url_config uses Env.DB_SCHEMES and not cls.DB_SCHEMES so you have to modify Env.DB_SCHEMES in place 😢