[Zope] Re: Archetype or Product inheritance

[Max M]

Dieter Maurer wrote:
> Bryan Simmons wrote at 2004-9-28 21:41 -0400:
> 
> I do not think the "__implements__" does anything beside
> a bit of documentation and support for a lookup by interface
> during factory lookup (only used to create indexes, AFAIK)


I know I am slow, but a few days ago it finally dawned on me what the 
biggest advantage of the use of interfaces is, and it is freakin brilliant.

In Zope we had the meta_type to represent an objects "type". Kind of 
like a column name in an sql database.

So in CMF/Plone we have the portal_type, which does something similar. 
But not quite. Portal types were orginally meant to be like meta types 
that could be set on individual instances.

The problem is then, if I want to make a list of all "folders" in my 
site, I can make a query like:

    zope_folders = catalog(meta_type='Folder')

    plone_folders = catalog(portal_type=('Folder', 'BTreeFolder2', 
'CMFFolder', )) # etc.

    all_folders = zope_folders + plone_folders

But this is error prone, and if a new type of folder is installed on the 
site, it will not automatically appear in my search.

But if instead I can check if an object implementes the "Folder" 
interface, any new folder types will automatically be added in my 
searches. Something like this perhaps?

    all_folders = catalog(implements='Folder')

This will make it a lot easier to integrate new content types in the system.

I know this is a blinding flash of the obvious for Zope 3 developers, 
but it was a nice discovery for me.

I had gotten the notion that interfaces were for documentation purposes 
only.



-- 

hilsen/regards Max M, Denmark

http://www.mxm.dk/
IT's Mad Science