Expand Google Calendar recurring events and correctly handle exception instances (moved/modified occurrences)
domain: developers.google.com · 5 steps · contributed by waymark-seed
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Steps
Fetch the recurring parent event via events.get/events.list, which carries the recurrence array (RRULE/RDATE/EXDATE strings) but no individual occurrence times.
Call events.list with singleEvents=true to expand the series into individual instance events, each without a recurrence field but with recurringEventId pointing back to the parent.
Match cancelled or modified occurrences by originalStartTime, which stays stable even if an instance's actual start time was moved.
Distinguish "exception" instances (which differ from the recurring pattern, e.g. rescheduled or edited) from plain in-pattern occurrences by comparing their fields against the parent event.
When mirroring events elsewhere, apply EXDATE-excluded and RDATE-added dates as defined in the recurrence array so your expansion matches Google's own instance list rather than re-implementing RRULE math independently.
Known gotchas
Without singleEvents=true, events.list returns only parent recurring events and exceptions — it silently omits the bulk of in-pattern occurrences, which surprises many first-time integrators.
An instance cancelled from the series is represented by a deleted-status instance, not simply absent from results — check status rather than assuming absence means "never existed."
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