[Chandler-dev] Future of redirectTo?

John Anderson john at osafoundation.org
Wed Jul 26 09:59:43 PDT 2006



Grant Baillie wrote:
>
> Sure. But how exactly would this work: i.e. onValueChanged(), 
> monitoring the changed values, or some other way? I'm a little wary of 
> onValueChanged() becoming overly complex. In general, we want to index 
> these attributes, so what I'd like to see is an API similar to what's 
> now pim.Calculated:
>
> class MyContentItem(ContentItem):
>
>    def getInterestingDatetime(self):
>        # ... perform possibly complex calculation
>        return resultOfPossiblyComplexCalculation
>
>    # optional: setInterestingDatetime
>
>    interestingDatetime = schema.IndexedProperty(
>                                   schema.DateTime,
>                                   basedOn = ('startTime', 'ticklers'), 
> # basedOn == attributes in Indexed.addIndex()
>                                   indexType = 'attribute', # could be 
> 'string',
>                                   fset = getInterestingDatetime)
>
> This would create an attribute which is a property on the class, and 
> also create the appropriate index (named the same as the attribute). 
> Maybe it somehow caches the value so that getInterestingDatetime 
> doesn't get called every time the attribute is accessed (though it's 
> not clear that's necessary).
>
> (FWIW, it's the index that ends up creating a monitor here to update 
> when changes are made to the "source" attribute).
>
I'm also not in favor of using onValueChanged.

A simple implementation possibility would be to use a python property 
for each source attribute involved in the complex calculation. It would 
set the source attribute and call the complex calculation method that 
might update the indexed attribute.


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