Stephen Masterman wrote:
Does ZODB have something equivalent to Durus' Computed Attributes? Which
I understand are attributes (or methods) on a Persistent object that
compute a value from some other attributes and then cache that result
for each connection, and if any of the attributes from which the
Computed Attribute computes its result change, the new result will be
automatically computed and all connections will have their cached value
invalidated.


Zope 2 has ComputedAttribute. It allows you to access the result of a method as an attribute:


from ComputedAttribute import ComputedAttribute
import ExtensionClass

class Example(ExtensionClass.Base):

    def _anAttribute(self):
        return 'foo'

    anAttribute = ComputedAttribute(_anAttribute)

>>> example = Example()
>>> example.anAttribute
'foo'
>>>


On a related note, do properties work with Persistent objects in ZODB? I
mean the Python property() function. I do not know how it interacts with
__getattr__() and stuff, and I know the ZODB docs warn against messing
with those functions for Persistent classes. If they do work, do they
basically serve as a non-cached computed attribute? Is a Durus Computed
Attribute just a property with caching and consistency for multiple
connections? (I know this isn't a Durus list.)

For your information:
property() doesn't work for ExtensionClass bases classes. You can't use them in Zope 2 up to 2.7. Python properties are working with ZODB 3.3+ (Zope 2.8 and Zope3).



Christian _______________________________________________ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/

ZODB-Dev mailing list  -  ZODB-Dev@zope.org
http://mail.zope.org/mailman/listinfo/zodb-dev

Reply via email to