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chris37170
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Lower Saxony
Joined: Dec 10, 2017
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After a date shift, the appointment appears twice	Reply to this Post Reply with Quote
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Hello

I moved an appointment in March in the Google calendar from 03/09/2018 to 03/02/2018. This date will also be displayed correctly in Google calendar. In the localendar, however, this appointment appears twice. Once the new appointment 03/02/2018 and also the original date 03/09/2018.

sincerely

Christoph
user: chris37170

(Translated with google translator)

[Dec 15, 2017, 12:55:25 PM] [37.4.237.115]

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support
localendar Expert

Joined: Aug 9, 2022
Posts: 6395
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Re: After a date shift, the appointment appears twice	Reply to this Post Reply with Quote
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This is what the event looks like in the feed we are receiving from Google:

BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20180302T190000
DTEND;TZID=Europe/Berlin:20180302T230000
DTSTAMP:20171215T232609Z
UID:3dhhkrpog3u6scjq7883vpfg88@google.com
RECURRENCE-ID;TZID=Europe/Berlin:20180309T190000
CREATED:20170921T081032Z
DESCRIPTION:
LAST-MODIFIED:20171215T121148Z
LOCATION:DGH Dinkelhausen
SEQUENCE:1
STATUS:CONFIRMED
SUMMARY:FFW: Seniorengruppe Klönabend
TRANSP:OPAQUE
END:VEVENT

Please note this line:

RECURRENCE-ID;TZID=Europe/Berlin:20180309T190000

Google appears to be indicating there is still an occurrence on 9 Mar 2018
The specification for how to handle RECURRENCE-ID is not clear. At this time, localendar will assume these events should be displayed.

If you delete the event in Google and re-create it (instead of Move), it may work properly
----------------------------------------
Marc Higgins
Support Associate, localendar.com
Follow us on Twitter! http://www.twitter.com/localendar_news

[Dec 15, 2017, 11:36:34 PM] [69.126.188.75]

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chris37170
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Lower Saxony
Joined: Dec 10, 2017
Posts: 8
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Re: After a date shift, the appointment appears twice	Reply to this Post Reply with Quote
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Hello Marc,

The deadline of 03/09/2017 is a recurring appointment that takes place every two months (January, March, May, July, September, November) every second Friday of the month. By postponing the deadline from 03/09/2017 to 03/02/2017, Google calendar has marked this recurring event with the flag RECURRENCE-ID. This flag must not be taken into account for entries in the localendar.
I hope you can take this into account.

Translated with Google translator

Sincerly

Christoph

[Dec 16, 2017, 5:22:36 AM] [37.4.237.115]

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support
localendar Expert

Joined: Aug 9, 2022
Posts: 6395
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Re: After a date shift, the appointment appears twice	Reply to this Post Reply with Quote
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The handling of RECURRENCE-ID is unfortunately not as standardized as you would hope. There are also other ways to handle event exceptions in iCal.

The current library we are using for iCal parsing does not follow the same interpretation Google is using this field for. At this time, we are limited in how we can handle this use of RECURRENCE-ID
----------------------------------------
Marc Higgins
Support Associate, localendar.com
Follow us on Twitter! http://www.twitter.com/localendar_news

[Dec 21, 2017, 2:33:26 AM] [69.126.188.75]

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chris37170
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Lower Saxony
Joined: Dec 10, 2017
Posts: 8
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Re: After a date shift, the appointment appears twice	Reply to this Post Reply with Quote
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Hello Marc,

I found this links to this problem. Maybe it helps.

https://icalendar.org/iCalendar-RFC-5545/3-8-4-4-recurrence-id.html
https://www.kanzaki.com/docs/ical/recurrenceId.html

Sincerely and nice Christmas

Christoph

[Dec 24, 2017, 5:13:28 AM] [37.4.237.115]

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support
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Joined: Aug 9, 2022
Posts: 6395
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Re: After a date shift, the appointment appears twice	Reply to this Post Reply with Quote
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Thanks,

We're aware of the specs you mention, but as I noted in my last post, what the specs say and how others have chosen to implement it are two separate items wink

Since we are not internally ical-based, we rely on 3rd party libraries to help where we integrate with iCal feeds. And at this time, the handling of RECURRENCE-ID is slim to none.

Just two of many public threads where people are wrangling with this issue (this time from a Wordpress calendar provider) https://icalevents.com/4437-correct-handling-of-uid-recurrence-id-sequence/
also https://stackoverflow.com/questions/11456406/recurrence-id-in-icalendar-rfc-5545

IBM has this to say about the subject (I have added emphasis)

RECURRENCE-ID: This is a simple property, but is often misunderstood and is very important... particularly when updating a calendar entry.
RECURRENCE-ID refers to the ORIGINAL starting time for a single instance of a repeating meeting. If a meeting instance changes, its RECURRENCE-ID does NOT change... just its DTSTART and DTEND change.
It may be difficult to determine the RECURRENCE-IDs that represent instances identified in an RRULE. For the first instance, this is the DTSTART. IBM does not currently provide the ability to get a list of RECURRENCE-IDs in the initial release, but this can be done via interpretation of the RRULE.
Also, while a recurrence ID may specify a range (this and future), this is not currently supported by the API in any way. The reason for this is because other implementations (like Outlook) do not honor this and there are some ambiguities in the standard regarding the use of this. Our API only accepts or outputs single instance exceptions.

When localendar first started (in 1999!) iCal was a spec followed/used by basically no one. In the past 18 years (!!!) we have seen things mature to the point where it's a standard that works in about 95% of all cases. It's amazing the amount of interoperability and portability we have now compared to what we had back then. We'll continue to monitor the situation, and if everyone settles on a common implementation for RECCURENCE-ID, then we'll support it, too.
----------------------------------------
Marc Higgins
Support Associate, localendar.com
Follow us on Twitter! http://www.twitter.com/localendar_news

[Jan 1, 2018, 4:54:18 PM] [69.126.188.75]

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