[Zope-dev] How is 'retrieveItem intended to work with TTW Specialists?

25 Sep 2000

      Hello ZPatterns Folk.....

I'm trying to implement 'delagation' with a custom Specialist. The idea,
(I think this is one of the goals of ZPatterns... to allow delegation
of responsibility after the Framework is built...) 

I have:

a) MarketItemManager (Python subclass of Specialist) Some of methods, both DTML Methods,
   and plain old Python Methods, are *meant* to be acquire by the objects (DataSkins)
   he manages.

b) ThingManager (ZClass subclass of Specialist). This is really just a test
   class that is supposed to represent some later developer integrating
   my ZPattern based EMarket into their application, (e.g., inventory or
   whatever...)

in MarketItemManager I've defined a 'retrieveItem' (this would really be
done by the integrator...) that does something like this:

<dtml-return "myGreatSite.ThingSpecialist.getItem(key)">

with the hope that when the Specialist class gets traversed 
it will execute:

    def __bobo_traverse__(self, REQUEST, name):
        ob = getattr(self, name, _marker)
        if ob is _marker:
            ob = self.getItem(name)  <--- traversal invokes getItem....
            if ob is not None:
                return ob
            raise 'NotFound'
        return ob

    def getItem(self, key):
        """Get an item"""
        if hasattr(self.aq_base,'retrieveItem'):       <--- getItem invokes retrieveItem
            return self.retrieveItem(key=key) # XXX need DTML check?

        for rack in self.rackList:
            item = rack.__of__(self).getItem(key)
            if item is not None: return item

So my retrieve item gets called..... *unfortunately* it gets
called without any namespace parameter... so my retrieveItem
DTML method has no way to acquire a namespace so that it can
delagate to something else! 

So... here is what I did... I defined a method in my Python
subclass of Specialist..

class MarketItemManager(ZPatterns.Specialists.Specialist):
    """A Market Item Manager"""

    # Specify a name for the item type:
    meta_type='MarketItemManager'

    def retrieveItem(self, key):
        """ get an item...."""
        return self.__of__(self).delegateRetrieve(self, None, key=key)

Then I made a DTML method called 'delegateRetrieve' like so:

<dtml-return "myGreatSite.ThingManager.getItem(key)">

this way, my integrator can edit 'delegateRetrieve' to point
to whatever Specialist he wants to... and I have a Python
implementation of retrieveItem.

Does this sound OK? Am I working way too hard here? 
(I feel like I am! ;-> )

thanks,
-steve

[Zope-dev] How is 'retrieveItem intended to work with TTW Specialists?

Steve Spicklemire