[Chandler-dev] about pure occurrences

[Andi Vajda]

  Grant, Jeffrey,

Tonight it occurred to Grant and I that we were needlessly indexing and 
reindexing pure occurrences in the master indexes Bryan creates on the 
ContentItem kind collection for the dashboard.

>From what I could gather, the definition of a pure occurrence is a 
ContentItem instance that has a non None value for 'occurrenceFor' and a None 
value for 'modificationFor'.

Assuming that is correct, I changed the contentItems collection to be a 
FilteredCollection based on the ContentItem KindCollection and, once I got it 
right, was surprised to see that it made little or no difference in my import 
case.

Digging a little further, I see that *all* occurrences created when importing 
an .ics file or restoring cosmo collections are impure, they all have a non 
None value for 'modificationFor'. The only time I was able to create pure 
occurrences was by scrolling the calendar back and forth by some weeks.

Is it expected that all imported occurrences have a 'modificationFor' value ?

Andi..

ps: still, making this change does improve performance of operations involving
     pure occurrences as these are no longer indexed and reindexed.