Christophe Combelles a écrit :
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
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
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
__getattr__ retrieve the ICompanyType interfaces from the object
__setattr__ calls noLongerProvides then alsoProvides to change the interfaces.
then I have a Vocabulary which creates terms from all the interfaces whose type
is ICompanyType, and I use this vocabulary with a list+choice field and a
This way, the admin users can directly change the interfaces provided by company
objects, so that the menu and UI can automatically adapt to it.
However, I wonder the following: if an interface that defines some attributes is
first assigned to an object, then this attributes are written, then the
interface is removed and replaced by another one (eg: client that becomes a
provider), what will the first attributes become?
BTW, there is a problem with custom_widget and MultiCheckBoxWidget:
MultiCheckBoxWidget has to be wrapped in a custom widget to correctly set the
number of arguments.
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