Django support

Django is a popular web framework written in Python. Using DCI (or just roles) in Django is quite easy, but since Django is using some meta classes of its own, a few things have to be taken into account.

First of all, roles that need to be applied to model classes (which is most obvious) should use roles.django.ModelRoleType as metaclass.

>>> from roles.django import ModelRoleType               

Then roles can be applied in the regular way.

>>> class MoneySource(metaclass=ModelRoleType):          
...
...    def transfer(self, amount):
...        if self.balance >= amount:
...            self.withdraw(amount)
...            context.sink.receive(amount)

Since the roles module changes the class names (it adds the roles that are applied at a certain time), those can not be used directly for storing. For now, saving objects should be done outside the role context.

>>> class TransferMoney:                                 
...
...     def __init__(self, source, sink):
...        self.source = source
...        self.sink = sink
...
...     def transfer_money(self, amount):
...         """
...         The interaction.
...         """
...         with context(self,
...                     source=MoneySource,
...                     sink=MoneySink):
...             # Let roles interact, in context
...             self.source.transfer(amount)
...         # Do storage when roles are removed
...         self.source.save()
...         self.sink.save()