On Mar 20, 2008, at 11:04 PM, Sean Allen wrote:
I've been playing with this and I'm still having a disconnect 3 week
1. I love the zc.relation stuff it answers one area of stuff I
hadn't even gotten to yet.
2. I'm just totally missing something
less cool. :-/
If I have Customers and Orders and I want to be able update all of
them independently of their relationships ( so that if an order is
updated, when i get the customer at some later time, it has the
updated order amongst that relation ) but I can't figure it out. I
tried looking at the zope.app.folder stuff but I keep getting lost
in the zope aspects of it and am having a hard time seeing the
forest for the trees.
Is there some more general ready on the patterns used that you know
of? I think if I understood the idea more in an abstract sense, I
could get a lot more out of the folder implementation.
Here's a simple, dumb example that parallels the folder stuff. See
the Dict class in http://svn.zope.org/zc.async/branches/dev/src/zc/async/utils.py?rev=84657&view=auto
. You put something in the dict, and __setitem__ slams a name and a
parent. The other mutating methods should do the right thing as well
in terms of updating the back reference. So, completely randomly and
arbitrarily, but to try and make a parallel, what if customers were a
dict of orders, and when you made an order it was associated with only
one customer, and you put the order "in" the customer. This may be
bizarre--what's the key? can more than one customer be associated
with an order? But that would mean that customer.values() would get
all of the customer's orders, and order.parent would be the associated
This example subclasses zc.dict, a super simple package that only
depends on ZODB, btw. It does not have full dict behavior, as Jim
likes to point out, because items are stored by BTree sorting, not
hashes, but it looks like a dict otherwise. Maybe it can help you
out. If you want to try out this example, copy the code out and get
the zc.dict egg and give it a try.
Anyway, this pattern of directly manipulating back-references is good
for intrinsic relationships like customers and orders.
Hope that helps a bit,
For more information about ZODB, see the ZODB Wiki:
ZODB-Dev mailing list - ZODB-Dev@zope.org