[Dev] item collection decisions

[Grant Baillie]

On Jun 30, 2005, at 23:24, Ted Leung wrote:
>> 7. How will queries work on collections?
>>
>> For instance, if the calendar wants to query all items in a  
>> collection, within a given date range?
>>
>> Decision
>>
>> Collections will be first class citizens with respect to queries -  
>> you'll be able to pass them in as parameters to queries, such as:
>> query = MakeQuery("for i in '%s' where i.startDate <= '3/3/2005  
>> 03:15", collection)
>> (Ted, did I get this right?
> A Query is a predicate applied to a Set/Collection of items.   In  
> the new world, you will be able to apply predicates to any  
> collection of item.  At the moment this  happens via a  
> FilteredCollection kind which accepts the predicate as an  
> argument.  Right now my intention is to support the predicate  
> language from the existing Query implemenatation.  I have a feeling  
> the Phillip may be interested in something more Pythonic, which may  
> also be a possiblity.   Concretely:
>
> c = UserCollection(.....)
> fc = FilteredCollection(c, "i.startDate < '3/3/2005 03:15'")
>
> fc is itself a collection and can be used anywhere a collection  
> would be used.
>
> The existing query classes will go away, to be replaced by  
> FilteredCollections of other types of Collections.
>
>> 8. How will the autogeneration of recurring items happen?
>>
>> We need a mechanism so that if you query a collection on a given  
>> date range, the appropriate recurring items are created.
>>
>> Decision
>>
>> Ted is trying to make a pluggable system so that when a given  
>> attribute (or is it Kind?) is searched, a callback mechanism can  
>> be triggered to allow the creation of the items before the query  
>> actually runs, so the query finds them.
> I believe that this is feasible but have not worked out the precise  
> details.

My understanding of the recurrence spec is that CalendarEventMixin  
has a method

getOccurrencesBetween(start, end) -> check for virtual events that  
end after start and start before end, create any that don't already  
exist, return an iterable of events ordered by startTime

In the given case, don't we just need to run this on each calendar  
event in the collection we're given? i.e. adding a "pregeneration"  
callback API, and compiling a query, seem overly complex to me. (Of  
course, there are plenty of other use cases for FilteredCollections).

--Grant

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