On Mar 21, 2008, at 8:41 PM, Gary Poster wrote:
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 later.
1. I love the zc.relation stuff it answers one area of stuff I
hadn't even gotten to yet.
cool :-)
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=84657view=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 customer.
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.
Ok, I can see how this makes sense for the simple example I gave. You
can get all the info you need for any contained items by starting from
the customer.
That part I was already seeing but hadnt fully put it together because
I was distracted by the bigger complication part that keeps my brain
churning.
Let me give a more detailed example of where I hit a problem ( I'm
still leaving some stuff out, just trying to get the general map of
things here ):
Customer
name
has many addresses
has many orders
has many paymethods
Order
name
total
salestax
has many items
belongs to customer
LineItem
quantity
has a product
belongs to order
Product
sku
description
In this example if we have 3 Products w/ skus of:
Widget A
Widget B
Widget C
And we want to change the the description of Widget B and have that
change appear for everything, how do I do that?
basically, I want all LineItems for Widget A to all refer to a single
instance of Product. In a relational database,
that is easy... there are 3 entries in the Products table and there
is a foreign key in LineItems. Here, I have no idea how
to handle. Which makes me think that I'm missing some fundamental point.
I'm sure the answer to this will start a whole slew of new questions,
so thanks in advance for the help with this and
going forward. Its very frustrating to keep beating my head against
these conceptual points that I'm just not getting.
Usually, I have eureka moments after spending this much time on
something, this time, its just not coming.
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