[Kde-pim] Recurring entries in Calendars, with exceptions

[Shaheed Haque]

I'm vaguely nervous about the looseness of the coupling, as I there
are things which I would *love* to see such as the ability to undo an
exception - i.e. return a recurrence to its virginal state - which I
don't think any clients do today. Clearly that isn't an insoluble
problem, so I am content that we follow the standards-based model.

Question: since I don't even have control over or access to the
recurrence-id, what do I do for now (if anything)?

On 19 March 2012 23:15, Christian Mollekopf <chrigi_1 at fastmail.fm> wrote:
> On Monday 19 March 2012 20.22:32 Shaheed Haque wrote:
>> Hi,
>>
>> On 19 March 2012 08:50, Christian Mollekopf <chrigi_1 at fastmail.fm> wrote:
>> > On Sunday 18 March 2012 10.21:10 Shaheed Haque wrote:
>> >> David, thanks for confirming; I expect this is based on the notion of
>> >> recurrence that is in RFCs. In principle, I assume that we could
>> >> extend the EXDATE property with an X-param. Could the programming
>> >> model for the RecurrenceRule be extended to support this? I guess
>> >> korganizer would also have to understand the additional semantics, but
>> >> being able to save and restore the data would be a first step.
>> >>
>> >> Kevin, as I hinted, I suspect this is how Exchange represents things
>> >> internally. Certainly representing the innards in this way would give
>> >> complete flexibility.
>> >
>> > The standard way to do this in iCal is not to exclude & add a new Event,
>> > but to make use of RecurrenceID. This allows to add an event, matching a
>> > specific date of the recurrence-set using RecurreneceID, to change
>> > properties of either only that occurrence, or also all future events if
>> > THISANDFUTURE is set.
>> >
>> > https://tools.ietf.org/html/rfc5545#section-3.8.4.4
>> >
>> > Excluding and adding a new event is a bit of a hack because you loose the
>> > information that the event belongs to the recurrence.
>>
>> So, the idea is to "hook" the overriding entry to an instance of the
>> recurring entry - sounds interesting. Now, I'm probably not
>> understanding, but if we don't have an exclusion, then does the
>> Calendar program not show both the original instance and also the new
>> overriding entry? Or is it expected to have logic to do the right
>> thing here?
>
> The exception replaces the original event (respectively that specific
> occurrence, or also all future occurrences).
>
> The logic to expand recurrences is according to the rfc as follows.
>
> * Derive recurrence set from the recurrence-rule and start-date
> * Add further recurrence dates contained in the recurrence-date property
> * Remove exceptions from the exception-date property.
> * Apply changes from Recurrence exceptions matching a Recurrence ID (where a
> recurrence exception really just is a normal event which has a recurrence id).
>
> So KCalCore should notice if there are several events with the same UID, look
> for the Recurrence-ID in one of the conflicting events (which marks the
> exception), and then apply the exception at the specific occurrence specified by
> the recurrence-id.
>
> I don't think that's possible right now, but if we need that feature we should
> implement it according to the RFC.
>
> You can read that information more in detail in the chapters:
> * https://tools.ietf.org/html/rfc5545#section-3.8.4.4
> * https://tools.ietf.org/html/rfc5545#section-3.8.5
>
> Or my simplified take at it:
> http://wiki.kolab.org/User:Mollekopf/Drafts/KEP:17#Recurrences
>
> Cheers,
> Christian
>
>>
>> > Cheers,
>> > Christian
>> >
>> >> 2012/3/18 Kevin Krammer <krammer at kde.org>:
>> >> > On Sunday, 2012-03-18, Shaheed Haque wrote:
>> >> >> Hi,
>> >> >>
>> >> >> I've been looking into how Exchange handles exceptions to recurring
>> >> >> Calendar entries, and trying to map them to KCalCore. The basic notion
>> >> >> of having an Event with recurrences works fine, but the only support I
>> >> >> see for defining exceptions is to addExRule(RecurrenceRule). This is a
>> >> >> relatively poor fit for Exchange which support changes to the subject,
>> >> >> location and all sorts of other properties. OTOH, an exception in
>> >> >> Exchange has no ability to recur itself, which a RecurrenceRule can
>> >> >> clearly handle.
>> >> >>
>> >> >> Roughly speaking, an exception in Exchange is a cut-down one-off
>> >> >> Event, rather than a RecurrenceRule.
>> >> >>
>> >> >> Have I misunderstood how to use what is there, or are there any plans
>> >> >> to change the way exceptions work to allow them to have richer
>> >> >> semantics along the lines that Exchange supports?
>> >> >
>> >> > Would it be possible to add a recurrence exception so that the usual
>> >> > event
>> >> > does not appear of the specific date and additionally add a new child
>> >> > event for just that date?
>> >> >
>> >> > Cheers,
>> >> > Kevin
>> >> >
>> >> > --
>> >> > Kevin Krammer, KDE developer, xdg-utils developer
>> >> > KDE user support, developer mentoring
>> >> >
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