django-strategy-field

Set of custom fields useful to implement the Strategy Pattern with Django models.

The Strategies are displayed in SelectBoxes as standard choice field

This package provides the following custom fields:

• StrategyField
• MultipleStrategyField
• StrategyClassField
• MultipleStrategyClassField

The StrategyField can be accessed as instance of the model with an attribute context that points to model that 'owns' the field (inverse relation). So:

Example

from strategy_field.fields import StrategyField
from django.core.mail.backends.filebased.EmailBackend


class Event(models.Model):
    backend = StrategyField()

Event(sender='django.core.mail.backends.filebased.EmailBackend')

Use case

As example we can imagine an application that manages Events that need to be notified to users. Each Occurrence of Event can be notified using different transport, (email, sms,...). We want to be able to add/change the way we send notification, per event basis, simply using the Django admin panel.

from strategy_field.fields import StrategyField
from strategy_field.registry import Registry

class TransportRegistry(Registry)
    pass

class AbstractStrategy(object):
    def __init__(self, context):
        self.context = context

    def send(self):
        raise NotImplementedError

class EmailStrategy(AbstractTransport):
    def send(self):
        ...

class SMSStrategy(AbstractTransport):
    def send(self):
        ...
registry = TransportRegistry(AbstractStrategy)
registry.register(EmailStrategy)
registry.register(SMSStrategy)

class Event(models.Model):
    sender = StrategyField(registry=registry)

Event.objects.get_or_create(sender=EmailStrategy)
...
...
e = Event.objects.get(sender=EmailStrategy)
e.sender.send() # e.sender.context == e

More examples

Use callable

from strategy_field.fields import StrategyField
from strategy_field.registry import Registry

registry1 = Registry()
registry2 = Registry()

class A(model):
    sender = StrategyField(registry=lambda model: model._registry)
    class Meta:
        abstract = True

class C1(A):
    _registry = registry1
    class Meta:
        abstract = True

class C2(A):
    _registry = registry2
    class Meta:
        abstract = True

Project links

Stable
Development
Project home page:	https://github.com/saxix/django-strategy-field
Issue tracker:	https://github.com/saxix/django-strategy-field/issues?sort
Download:	http://pypi.python.org/pypi/django-strategy-field/