Re: [Twisted-Python] Woven: access to submodels

July 13, 2003

      On Sun, 13 Jul 2003, Mary <mary-twisted@puzzling.org> wrote:
...
1. Pure design issue: There still needs to be a query along the lines
 of "does this author in fact exist?" so that /author/Mary/ generates a
 list of my articles and /author/Humphrey/ generates an error page. This
 was the query I was trying to avoid by passing the submodel around --
 the "get me all posts by Mary" query was always going to be part of
 IndividualPage.
Ah, I see. Well, a somewhat thorny issue in current web code [that
we may fix someday in the future, but you're not interested in that]
is that child-getting is synchronous. This means that an easy answer
is currently beyond us. A non-easy way to do that is to hack around:

from twisted.web import resource, server

class MaybeIndividualPage(resource.Resource):

    isLeaf = 1

    def __init__(self, author):
        resource.Resource.__init__(self)
        self.author = author

    def render(self, request):
        def raiseException():
            raise LookupError
        def simulateServer(value):
            if value == server.NOT_DONE_YET:
                return
            request.write(value)
            request.finish()
        query = deferredWhichIsTrueIfExists(self.author).addCallback(
        lambda x: (x or error.NoResource()) and
             IndividualPage(self.author).getChildForRequest(request
                                            ).render(request)).addCallback(
            simulateServer)
        return server.NOT_DONE_YET

Then, in getDynamicChild, return MaybeIndividualPage(author) instead
of IndividualPage(author).

Basically, this is explicitly asyncing the child-getting mechanism
by going through the async-ready render method. I realize it's not
the best-looking code in the world, but it should get the job done.
...
2. More generally, since I'm unfamiliar with the design pattern(s)
 associated with Woven, what level of information sharing in this sense
 is acceptable between parents and children? (Pointers to other sources
 of information would be welcome, since this question is pretty open
 ended)?
Well, we don't have any real understanding of this issue either, since
Woven is not old enough. My gut instinct would be towards "pretty high",
though.

-- 
Moshe Zadka -- http://moshez.org/
Buffy: I don't like you hanging out with someone that... short.
Riley: Yeah, a lot of young people nowadays are experimenting with shortness.
Agile Programming Language -- http://www.python.org/