[Zope] Zope and Objects

[Mark McEahern]

[Jeff Childers]

> I'm starting to get the "big picture" but I'm still a little fuzzy
> on the details, particularly about objects and the ZODB. I'm hoping
> that someone can give me some brief pointers to where the answers
> the these questions lie. I have read a *bunch* of Zope doc and I'm
> pretty handy with Python.
> 
> 1) Where are data object classes defined in Zope?

I'm fairly new to Zope, although I've written some Zope Products.  My
sense is that there are two answers to your question:

  * ZClasses
  * Products

and that the best bet in the long-run, especially if you feel
comfortable with Python, is to skip ZClasses altogether and focus on
grokking Products.

> I get the persistent object thing. Very cool. So let's say I want to
> write a billing system. I have customer objects, invoice objects,
> and payment objects. [ Customer [ Invoices [Payments] ] ].

My guess is that you'd write a Product, BillingSystem.  The
BillingSystem Product would include a variety of classes:

  * A top-level container; e.g., Billing
  * Customer
  * Invoice
  * Payment

Only the top-level container would be addable to other Zope containers
(folderish objects).  Once you adding an instance of Billing, it would
have a slightly customized manage_main (I'm probably misspelling
that).  From Billing's manage_main, you could add Customers.  From a
Customer's management screens, you could add Invoices.  And so on.

> a) Where do I put the code that defines each custom class?  Scripts
> seem to be for def-functions. Do I have to put this outside Zope?

Yes, that's your best bet.  The common wisdom seems to be: Write this
as if it's just Python, then add a light wrapper for Zope.  Of course,
the devil can sometimes be in the details.

> b) Do I use ZCatalogs to 'index' my objects so I can query them
> similar to SQL? If so, how/where do I add my custom classes to the
> ZCatalog?

Good question.

> 2) How do I instantiate and persist (through the session) a
> particular instance of the class from the ZODB (i.e. a certain
> customer)?

The thing about PersistentObject is that you don't really have to do
anything for it to persist aside from instantiating it in Zope.  Isn't
that cool?

> I realize these are big questions. Any pointer toward answers, even
> which documentation I should be reading, would be helpful and
> greatly appreciated.

I think the short answer is that you want to investigate Products.

I'm hoping someone more knowledgeable about the specifics follows up.

Cheers,

// m
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