Group fanouts by id's

[erdtsieck]

Whenever you specify identities like this

Identities<ConsultationPickedUp>(x => x.PermanentParticipants.Concat(x.DetachedParticipants).ToList());

And fanout that event to two different events like this:

FanOut<ConsultationPickedUp, ConsultationRemovedForUser>(x => 
    x.Data.DetachedParticipants.Select(participantId => 
        new ConsultationRemovedForUser(participantId, x.StreamKey!)));
 FanOut<ConsultationPickedUp, ConsultationPickedUpForUser>(x =>
    x.Data.PermanentParticipants.Select(participantId => 
        new  ConsultationPickedUpForUser(participantId, x.StreamKey!)));

but should conditionally map to either one or the other, that is not possible at the moment. So it would ne beneficial to group fanouts to specific identities similair to void AddEvents<TEvent>(Func<TEvent, TId> singleIdSource, IEnumerable<IEvent> events) on a custom grouper.

Such as:

FanOut<ConsultationPickedUp, ConsultationRemovedForUser>(
    x => x.UserId, // group key on fanout event, consistent with ITenantSliceGroup.AddEvents() 
    x => x.Data.DetachedParticipants.Select(participantId => 
        new ConsultationRemovedForUser(participantId, x.StreamKey!))
);

[mysticmind]

Moving this to discussions