# Backends

Constance ships with a bunch of backends that are used to store the configuration values. By default it uses the Redis backend. To override the default please set the `CONSTANCE_BACKEND` setting to the appropriate dotted path.

## Redis

The configuration values are stored in a redis store and retrieved using the redis-py library. Please install it like this:

    pip install django-constance[redis]

Configuration is simple and defaults to the following value, you don’t have to add it to your project settings:

    CONSTANCE_BACKEND = 'constance.backends.redisd.RedisBackend'

Default redis backend retrieves values every time. There is another redis backend with local cache. CachingRedisBackend stores the value from a redis to memory at first access and checks a value ttl at next. Configuration installation is simple:

    CONSTANCE_BACKEND = 'constance.backends.redisd.CachingRedisBackend'
    # optionally set a value ttl
    CONSTANCE_REDIS_CACHE_TIMEOUT = 60

### Settings

There are a couple of options:

#### `CONSTANCE_REDIS_CONNECTION`

A dictionary of parameters to pass to the to Redis client, e.g.:

    CONSTANCE_REDIS_CONNECTION = {
        'host': 'localhost',
        'port': 6379,
        'db': 0,
    }

Alternatively you can use a URL to do the same:

    CONSTANCE_REDIS_CONNECTION = 'redis://username:password@localhost:6379/0'

#### `CONSTANCE_REDIS_CONNECTION_CLASS`

An (optional) dotted import path to a connection to use, e.g.:

    CONSTANCE_REDIS_CONNECTION_CLASS = 'myproject.myapp.mockup.Connection'

If you are using django-redis, feel free to use the `CONSTANCE_REDIS_CONNECTION_CLASS` setting to define a callable that returns a redis connection, e.g.:

    CONSTANCE_REDIS_CONNECTION_CLASS = 'django_redis.get_redis_connection'

#### `CONSTANCE_REDIS_PREFIX`

The (optional) prefix to be used for the key when storing in the Redis database. Defaults to `'constance:'`. E.g.:

    CONSTANCE_REDIS_PREFIX = 'constance:myproject:'

#### `CONSTANCE_REDIS_PICKLE_VERSION`

The (optional) protocol version of pickle you want to use to serialize your python objects when storing in the Redis database. Defaults to `pickle.DEFAULT_PROTOCOL`. E.g.:

    CONSTANCE_REDIS_PICKLE_VERSION = pickle.DEFAULT_PROTOCOL

You might want to pin this value to a specific protocol number, since `pickle.DEFAULT_PROTOCOL` means different things between versions of Python.

#### `CONSTANCE_REDIS_CACHE_TIMEOUT`

The (optional) ttl of values in seconds used by CachingRedisBackend for storing in a local cache. Defaults to 60 seconds.

## Database

Database backend stores configuration values in a standard Django model. It requires the package django-picklefield for storing those values.

You must set the `CONSTANCE_BACKEND` Django setting to:

    CONSTANCE_BACKEND = 'constance.backends.database.DatabaseBackend'

Please make sure to apply the database migrations:

    python manage.py migrate

Note

If you’re upgrading Constance to 1.0 and use Django 1.7 or higher please make sure to let the migration system know that you’ve already created the tables for the database backend.

You can do that using the `--fake` option of the migrate command:

    python manage.py migrate database --fake

Just like the Redis backend you can set an optional prefix that is used during database interactions (it defaults to an empty string, `''`). To use something else do this:

    CONSTANCE_DATABASE_PREFIX = 'constance:myproject:'

### Caching

The database backend has the ability to automatically cache the config values and clear them when saving. Assuming you have a `CACHES` setting set you only need to set the the `CONSTANCE_DATABASE_CACHE_BACKEND` setting to the name of the configured cache backend to enable this feature, e.g. “default”:

    CACHES = {
        'default': {
            'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
            'LOCATION': '127.0.0.1:11211',
        }
    }
    CONSTANCE_DATABASE_CACHE_BACKEND = 'default'

Warning

The cache feature won’t work with a cache backend that is incompatible with cross-process caching like the local memory cache backend included in Django because correct cache invalidation can’t be guaranteed.

If you try this, Constance will throw an error and refuse to let your application start. You can work around this by subclassing `constance.backends.database.DatabaseBackend` and overriding __init__ to remove the check. You’ll want to consult the source code for that function to see exactly how.

We’re deliberately being vague about this, because it’s dangerous; the behavior is undefined, and could even cause your app to crash. Nevertheless, there are some limited circumstances in which this could be useful, but please think carefully before going down this path.

Note

By default Constance will autofill the cache on startup and after saving any of the config values. If you want to disable the cache simply set the `CONSTANCE_DATABASE_CACHE_AUTOFILL_TIMEOUT` setting to `None`.

## Memory

The configuration values are stored in a memory and do not persist between process restarts. In order to use this backend you must set the `CONSTANCE_BACKEND` Django setting to:

    CONSTANCE_BACKEND = 'constance.backends.memory.MemoryBackend'

The main purpose of this one is to be used mostly for testing/developing means, so make sure you intentionally use it on production environments.