174a0ab4f1
git-svn-id: svn://svn.cy55.de/Zope3/src/cybertools/trunk@1540 fd906abe-77d9-0310-91a1-e0d9ade77398
102 lines
2.8 KiB
Text
102 lines
2.8 KiB
Text
==========================
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A Simple Adapter Framework
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==========================
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$Id$
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To work with adapters we need at least two classes, one for objects
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that we want to adapt to (the adapter's `context`) and one for the adapters.
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>>> class Content(object):
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... pass
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>>> class StateAdapter(object):
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... def __init__(self, context):
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... self.context = context
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... def setState(self, state):
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... self.context._state = state
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... def getState(self):
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... return getattr(self.context, '_state', 'initial')
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In order to use the adapters in a flexible way we create adapter objects
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by using an adapter factory. The stateful factory is intended to create
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adapters that allow setting and retrieving the state of objects.
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>>> from cybertools.util.adapter import AdapterFactory
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>>> stateful = AdapterFactory()
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We can now register our StateAdapter class with the `stateful` AdapterFactory.
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We have to tell the factory which class of adapted objects a certain
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adapter class is responsible for.
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>>> stateful.register(StateAdapter, Content)
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Now we are ready to create an object of the Content class
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>>> c1 = Content()
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and a corresponding `stateful` adapter:
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>>> c1State = stateful(c1)
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The adapter can now be used to access the Content object's state:
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>>> c1State.getState()
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'initial'
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>>> c1State.setState('visible')
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>>> c1State.getState()
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'visible'
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The procedure also works with subclasses of the Content class.
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>>> class SpecialContent(Content):
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... pass
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>>> sc1 = SpecialContent()
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>>> sc1State = stateful(sc1)
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>>> sc1State.getState()
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'initial'
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>>> sc1State.setState('public')
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>>> sc1State.getState()
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'public'
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But if we try to use an adapter factory for objects for which there is
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no adapter registered we get back None.
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>>> class UnknownContent(object):
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... pass
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>>> uc1 = UnknownContent()
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>>> uc1State = stateful(uc1)
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>>> uc1State is None
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True
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Class adapters as factories
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---------------------------
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There is a special case that can be handled with an adapter factory:
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creating objects via an adapter to a class. An example for this is
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a class that creates objects by loading them from a file or database,
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so this would be a storage adapter class.
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In our example we avoid reading from disk or from a database but just
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create the object wanted by using the context's constructor.
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>>> class ContentLoader(object):
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... def __init__(self, context):
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... self.context = context
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... def load(self):
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... return Content()
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>>> storage = AdapterFactory()
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>>> storage.register(ContentLoader, Content)
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In this case we get the adapter from the adapter factory by providing
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it with the context class (instead of an instance of it like in the
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example above.
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>>> loader = storage(Content)
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>>> c2 = loader.load()
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>>> c2
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<Content object ...>
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