[Zope3-Users] Re: ObjectModifiedEvent but not ContainerModifiedEvent

[Jeff Shell]

On Aug 17, 2007, at 5:29 PM, Chris Withers <chris at simplistix.co.uk>  
wrote:

> Martin Aspeli wrote:
>> def handler(event):
>>    if IContainerModifiedEvent.providedBy(event):
>>        return
>
>
> ...which is pretty inefficient.
>
> All the subscriber lookup, etc, has to happen to get this far.
>
> There must be a better way..

Well,

a container is an object.

It's being modified by the sake of its content changing.

So it makes sense that a container modified event is a specialized  
extension of object modified.

Better way? The only better way, really, would be doing a re-dispatch.  
Or fire off your own event when you modify other properties on a  
container.

Or kick all of the code that sends modified events so that they send  
along descriptions of what has changed. Sometimes I want to respond  
only when a Dublin core element has changed - ie, to clear a cache. I  
ended up writing a replacement for formlib's applyChanges so that it  
not only returns a true/false value if changes where made, but also a  
sequence of Modified descriptions for each changed field. Then when  
these are included with the modified event, I can do further filtering  
within my code to see what exactly changed.