Has anyone figured out how to accept the an invitation to an event from the event record? I can’t seem to find the link between the master event and child events for those invited via the EventRelation object. This object only points to the master event but the child event. Nor does the EventRelation object have any child relationships to the child events. Kinda stumped. Here’s what I have so far.

Article describing the same issue.
https://help.salesforce.com/apex/HTViewSolution?id=000199687&language=en_US

Article laying out the schema.
https://www.salesforce.com/developer/docs/api/Content/sforce_api_erd_activities.htm

I suspect the only solution is to query EventRelation based on the values in the Event for the current user only when the Event has IsGroupEvent and IsChild is true.
Event.OwnerId = EventRelation.RelationId
Event.Subject = EventRelation.EventId.Subject
Event.StartDateTime = EventRelation.EventId.StartDateTime
Event.EndDateTime = EventRelation.EventId.EndDateTime
Event.Description = EventRelation.EventId.Description
Event.WhatId= EventRelation.EventId.WhatId
Event.WhoId= EventRelation.EventId.WhoId
Event.AccountId= EventRelation.EventId.AccountId

In theory this would very very rarely been an issue as no one would make an Event that already exists with all the same attributes. Still, seems lame to me that this is the only way to do this.

Video showing the most I can get from the objects as I see it.