F. Oliver Gathmann wrote:
>
> On 11/12/09 1:00 PM, Tim Hoffman wrote:
>> Hi
>>
>> I have done some fairly extensive projects using traversal over a
>> relational model and we did use intermediate container classes alot.
>> Mainly because each major entity could have about 6 different classes
>> of sub items that we needed to group into containers anyway
>>
>> I reverse engineered the entire relational model from the existing
>> database and then autogenerated all of the intermediate classes.
>> Quite easy to do. I was using storm as an orm over the top, which
>> made things a lot easier
> Hmm... still, this feels like an artifact to me. Presumably, in most
> cases what you want to return when the URL asks for a collection of
> sub-items is the very collection you already defined in your ORM on the
> model object that is the current context (we are using SQLAlchemy, BTW).
> I cannot help but think that there should be a way to automatically
> return an adapted collection that supports further traversal if
> necessary... but I'm not sure of all the ramifications of that idea.
I suspect there should be a pattern for this. This pattern might be a good
one, though I don't know to what extent it can be generalized:
class TraversableCollection(object):
def __init__(self, parent, name, collection):
self.__parent__ = parent
self.__name__ = name
self.collection = collection
def __getitem__(self, name):
return getattr(self.collection, name) # or whatever the API is
class Cars(object):
def __getitem__(self, name):
collection = get_collection(model, name) # some helper thing
return TraversableCollection(self, name, collection)
Might be generalizable via a subclass:
class Collection(object):
def __getitem__(self, name):
collection = get_collection(model, name) # some helper thing
return self.collection_class(self, name, collection)
class Cars(Collection):
collection_class = TraversableCollection
Or via Zope-style adaptation.
- C
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