[Zope3-Users] Design question (object or interface for category implementation?)

[Garanin Michael]

Christophe Combelles wrote:
> Christophe Combelles a écrit :
>> Hi,
>>
>> I'm playing again with the notion of categories of objects.
>>
>> I have two main goals:
>> ---------------------
>> 1) I must let the user choose the category of an object added to the 
>> zodb. For this, I must be able to retrieve the list of categories and 
>> present them in a form field managed by a vocabulary (or in a 
>> different manner).
>> 2) I must have different behaviours for categorized objects:
>> objects of different categories would have different views, different 
>> addMenuItems (if they are containers), etc.
>>
>> the first requirement would tell me to define categories as objects, 
>> while the second one would tell me to define them as interfaces.
>>
>> The possible solutions I see:
>> ----------------------------
>>
>> 1) The simplest solution is to store the categories as text strings 
>> into the annotations of the object. So categories actually are just 
>> tags.
>>
>> 2) The second solution is to do the same, but replace text strings 
>> with category objects, that implement ICategory. And categories can 
>> be stored separately in a category container, or in a registered 
>> utility that gives the list of available categories. This is a bit 
>> better, but this way I don't know how to easily let my categorized 
>> objects behave differently according to their categories.
>>
>> 3) The third solution is to define categories as interfaces extending 
>> ICategory. I can retrieve the list of categories with 
>> ICategory.dependents
>> But to present them in a form, I must have a pretty name for each 
>> interface. Should I store them in a Tagged Value?
>>
>> 4) The fourth solution I see, is to define an interface type, 
>> ICategoryType, extending IInterface just like IContentType. Then my 
>> categories would be interfaces whose type is ICategoryType. But with 
>> IContentType, is there a way to retrieve the list of all available 
>> content types?
>
> I've finally mixed 3) and 4) :
>
> I have defined ICompany(Interface), IClient(ICompany), 
> IProvider(ICompany)
> And I have an ICompanyType(IInterface) interface type
> I've set the type of IClient and IProvider as ICompanyType in zcml.
>
> ICompany has a "types" attribute, for which I've redefined __getattr__ 
> and __setattr_:
> __getattr__ retrieve the ICompanyType interfaces from the object
> __setattr__ calls noLongerProvides then alsoProvides to change the 
> interfaces.
I think that it's not work: "alsoProvides" and "directlyProvides" change 
interfaces only in memory, it's not persistent changes (after restart 
Zope yours object will be only basic interface) .
(sorry my honor english).