Re: Object created events

Hi Kapil,


Kapil Thangavelu wrote:
> 
> i think this needs a proposal and to be thought through rather than code  
> just landing.
> 

Well, there was a big discussion and this is the continuation of that
discussion. :)



> i think created events are the wrong semantic, z3 fires them for class  
> instantiation/factory creation, and you want them for object  
> initialization in context, which are different use cases. i'd rather some  
> subclass of modified event for initializated that fired only once.
> 

That is exactly what I proposed:

 - IObjectCreatedEvent when the type is first created (in the constructor,
or initializeArchetype)
 - IObjectModifiedEvent on regular modifications
 - IContentInitializedEvent, inherits from IObjectModifiedEvent and is fired
(instead of IObjectModifiedEvent) on the first initialisation.



> also the point that rocky makes that this stuff shouldn't be in base AT  
> classes, is valid imho, z3 events are typically fired by view code and  
> putting inline with method calls, means like some serious headaches for  
> existing software. for example as soon you add in hacking in a few  
> modified events and hook up an indexer to it, you now have the fragile at  
> manager_after add dance, and api usage generating events, causing  
> indexing, resulting in extraneous duplicate indexation calls, which just  
> makes the system harder to assume any deterministic behavior for.  
> basically lots of code thats using the api isn't expecting to generate  
> events, is suddenly going to be generating events, and unless we have a  
> coherent story about moving AT to it, doing it piecemeal in adhoc fashion  
> is likely to be dentrimental and destabilizing, imo.
> 

I think these are valid points, but there are also clear benefits to having
a few sane, basic lifecycleevents - this stops us hacking into the API in
different ways.

The proposal here is that we fire in processForm() in the first instance,
which for all intents and puropses *is* view code. It's just that before
Zope 3 and Five came along, view code was stuffed into methods on the the
content class itself. processForm() is not really an API that people use
from non-view code, so I think this is safe.

About the creation event, initializeArchetype() ought to be safe, IMHO, but
other ideas are much appreciated.

Cheers,
Martin

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