"Phillip J. Eby" a écrit :
> At 08:39 PM 5/17/00 +0400, Jepthte CLAIN wrote:
> >
> >I wonder if someone can send me a simple example using the ZPatterns
> >framework. I read all the source, and I still can't figure out what is
> >the relationship between the objects instantiated by the Racks and the
> >Rackmountable objects. Also, why do the rack try to instantiate a
> >ZClass???
> When created, Racks create some default Attribute and Sheet providers.
> These objects are used by Rackmountables to access data which is not stored
> directly in the rackmountable.

Indeed, attribute and sheets are not stored in the rackmountable. Where
are they stored then? in the specialist? in the rack? reading the code
does not help to answer that question.

> When used, Racks create instances of the ZClass you've specified.  If you
> call newItem(key), you will receive a new instance of that ZClass, which
> will be stored in the rack under the specified key.  Whenever you call
> getItem(key), the instance will be retrieved.  Some Racks, like
> GenericUserSource, do not store items in themselves, but in external
> databases.  When you call getItem(key) on a GUS, it calls methods to access
> the external database, then creates an instance of the appropriate
> LoginUser subclass and returns that.
I don't like ZClasses, because I want to use XEmacs to edit my code.
In fact, I have trouble using a python class to store my data.

say I have in MyItem.py:

class MyItem(RackMountable, Item):
        meta_type = 'My Item'

        def __init__(self, id):
                self.id = id
                self.i = 0
                self.s = ''

and in __init__.py, MyItem is registered as a z base class

i and s are properties my objects are going to store. I would like to
use MyItem objects until I am ready to move the data into an SQL
database, where i and s will be columns in a table.

The AttributeProvider (that my rack have by default) raise an exception
in MyItem.__init__ because i and s do not exist (indeed, I want to
create them in the instance!)

Also, say I want to add the OFS.ProperyManager.PropertyManager mixin
class to MyItem to manage my properties through the standard interface.
Will it clash with the sheet provider?

> Hope that helps; I'm not 100% clear on your question.
Anyway, my question was not 100% clear neither :-)

I'm not interested in the ZPatterns framework to allow my customers to
customize the data sources or the collaborators. I'm interested in it
because I want to develop code that is independant of the data sources.
I want to store some data in the ZODB (because they are python list and
dict, or because it is easier for me to use Zope objects until I move to
a SQL database), and some of them in an SQL database (because they might
be used by externals applications), but still want to have a common
interface to the data.
I'm still figuring out how it works, but once I'm done, I will rule the
world :-)

Thanks for your good work, and thanks for the advices!
jephte clain

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