[Zope-CMF] Persistent dictionaries

[Dieter Maurer]

Thomas Olsen writes:
 > I'm working on a CMF Product which is based on PortalFolder and 
 > PortalContent. This Folderish object contains some items which inherits from 
 > OFS.SimpleItem.Item, Persistence.Persistent and Aquisition.Implicit.
 > These items have (had) some properties which are speciel to their class. In 
 > order to get around the problem with adding new attributes and having 
 > instantiated objects which doesn't have the attributes I decided to keep the 
 > attributes in a dictionary. So in my base class I did:
 > 
 > ---snip--------------------------------------------
 > class AbstractElement(Persistent, Item, Implicit):
 >     """ Abstract base class for Element objects. """
 >     _attributes = PersistentMapping()
 > 
 >     def __getattr__(self, name):
 >         if self._attributes.has_key(name):
 >             return self._attributes[name]
 >         else:
 >             raise AttributeError, name
 > ---snip--------------------------------------------
 > 
 > and my derived classes look something like this:
 > 
 > ---snip--------------------------------------------
 > class TextElement(AbstractElement):
 >     """
 >     text element.
 >     """
 >     meta_type = 'Text Element'
 > 
 >     def __init__(self, id):
 >         self.id = id
 >         self._attributes = {'value':'','html':'','alignment':''}
>From here on "self._attributes" is no longer a PersistentMapping
but a normal Python dictionary.
Internal modifications do not trigger the persistence machinery.
They would, if "_attributes" were still a PersistentMapping....


Dieter