django-waffle 0.7.6

Installation

To start using Waffle, you just need to add it to your INSTALLED_APPS and MIDDLEWARE_CLASSES, and make sure to add the request context processor:

TEMPLATE_CONTEXT_PROCESSORS = (
    # ...
    'django.core.context_processors.request',
    # ...
)

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

MIDDLEWARE_CLASSES = (
    # ...
    'waffle.middleware.WaffleMiddleware',
    # ...
)

Since Waffle will be setting cookies on response objects, you probably want it below any middleware that tweaks cookies before sending them out.

Flags, Switches and Samples

Waffle supports three separate but ultimately similar concepts: Flags and Switches, and Samples.

Basically, a Flag is tied to a request, while Switches and Samples are not. Consequently, Flags are much more complicated, while Switches are just a named boolean in the database, and Samples are just a percentage stored in the database.

Using Waffle

Flags and Switches can be used in templates, in views, or wrapped around entire views. Samples can be used in templates or views but not to wrap an entire view.

If you try to use a flag or switch that is not defined, it will always be inactive.

{% if waffle.flag('flag_name') %}
  Content if flag is active
{% endif %}

{% if waffle.flag('flag_name') %}
  Flag is active!
{% else %}
  Flag is inactive!
{% endif %}

{% if waffle.switch('switch_name') %}
  Content if switch is active
{% endif %}

{% if waffle.switch('switch_name') %}
  Switch is active!
{% else %}
  Switch is inactive!
{% endif %}

{% if waffle.sample('sample_name') %}
  Sample is active!
{% else %}
  Sample is inactive!
{% endif %}

{% load waffle_tags %}
{% flag flag_name %}
  Content if flag is active
{% endflag %}

{% flag flag_name %}
  Flag is active!
{% else %}
  Flag is inactive!
{% endflag %}

{% load waffle_tags %}
{% switch switch_name %}
  Content if switch is active
{% endswitch %}

{% switch switch_name %}
  Switch is active!
{% else %}
  Switch is inactive!
{% endswitch %}

{% sample sample_name %}
  Sample is active!
{% else %} {# Optional `else` section #}
  Sample is inactive!
{% endsample %}

import waffle

def my_view(request):
    if waffle.flag_is_active(request, 'flag_name'):
        # Behavior if flag is active.
    else:
        # Behavior if flag is inactive.

import waffle

def myview(request):
    if waffle.switch_is_active('myswitch'):
        return 'switch is active'
    return 'switch is inactive'

import waffle

def myview(request):
    if waffle.sample_is_active('mysample'):
        # Some percent of requests.

from waffle.decorators import waffle_flag

@waffle_flag('flag_name')
def my_view(request):
    # View only available if flag is active.

from waffle.decorators import waffle_switch

@waffle_switch('switch_name')
def my_view(request):
    # View only available if switch is active.

@waffle_flag('!flag_name')
def my_view(request):
    # View is only available if flag is INactive.

Global Settings

There are a few global settings you can define to adjust Waffle’s behavior.

WAFFLE_COOKIE:

The format for the cookies Waffle sets. Must contain %s. Defaults to dwf_%s.

WAFFLE_FLAG_DEFAULT:

When a Flag is undefined in the database, Waffle considers it False. Set this to True to make Waffle consider undefined flags True. Defaults to False.

WAFFLE_SWITCH_DEFAULT:

When a Switch is undefined in the database, Waffle considers it False. Set this to True to make Waffle consider undefined switches True. Defaults to False.

WAFFLE_SAMPLE_DEFAULT:

When a Sample is undefined in the database, Waffle considers it False. Set this to True to make Waffle consider undefined samples True. Defaults to False.

WAFFLE_MAX_AGE:

How long should Waffle cookies last? (Integer, in seconds.) See the Cookies section. Defaults to 2529000 (one month).

WAFFLE_OVERRIDE:

Whether Flags can be controlled from the query string. Defaults to False.

WAFFLE_SECURE:

Whether to set the secure flag on cookies. Defaults to False.

Overriding Flags

If you turn on the WAFFLE_OVERRIDE setting, you can guarantee a flag will be active for a request by putting it in the query string.

For example, if I use the flag example in a view that serves the URL /search, then I can turn on the flag by adding ?example=1 to the query string, or turn it off by adding ?example=0.

By default, WAFFLE_OVERRIDE is off. It may be useful for testing, automated testing in particular.

Switches cannot be overridden at this time.

Cookies

When falling back to percentage of active users, Waffle will set a cookie for every request, setting the flag’s value (on or off) for future requests.

If the cookie is set, its value is used (either True or False) and it is re-set. Since cookies are re-set on every request (that uses the flag), you do not need to set WAFFLE_MAX_AGE very high. Just high enough that a typical returning user won’t potentially flip back and forth between off and on.

Rollout Mode

Rollout Mode allows you to gradually enable a feature for all users. In “normal” mode, a flag’s value will be set in a cookie until WAFFLE_MAX_AGE whether the flag is active or not. In Rollout Mode, an inactive flag will set a session cookie, and an active flag will set a longer-lived cookie.

Every time a user starts a new session, they’ll have a chance (determined by the percentage of the flag) to have the feature turned on “permanently”. Once it’s on, it should stay on, unless they clear their cookies or use a different browser (see To Do).

To guarantee an even rollout, it will likely be necessary to gradually increase the flag’s percentage as more and more users get stuck with the active cookie.

Rollout Mode is enabled per flag.

Waffle in JavaScript

Waffle now helps you use flags directly in JavaScript. You need to add the wafflejs view to your urls.py:

from waffle.views import wafflejs

urlpatterns = patterns('',
    # ...
    url(r'^wafflejs$', wafflejs, name='wafflejs'),
    # ...
)

You can then load the Waffle JavaScript in your templates:

<script src="{% url wafflejs %}"></script>

Once you’ve loaded the JavaScript, you can use the global waffle object. Just pass in a flag name. As in the Python API, if a flag or switch is undefined, it will always be false.

if (waffle.flag('some_flag')) {
    // Flag is active.
} else {
    // Flag is inactive.
}

if (waffle.switch('some_switch')) {
    // Switch is active.
} else {
    // Switch is inactive.
}

if (waffle.sample('some_sample')) {
    // Sample is active.
} else {
    // Sample is inactive.
}

waffle.sample(foo) will return the same value on a given request but that value may not persist across multiple requests.

To Do

• Keep a flag setting for a given user, regardless of browser/device.