On 11/12/09 1:33 PM, Chris McDonough wrote:
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
Cool - this is exactly what I had in mind.
I am really impressed by the number and quality of the comments I got on
my little newbie question! Seems we made the right choice by basing our
new server framework on repoze.bfg ;-)
Cheers,
Oliver
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