Multiple projections per endpoint

To reduce the need to replace the entire endpoint stream every upgrade - lets create projections for each namespace value in [Versioned] events and subscribe to each.

Then, a replay would only be needed for the specific projection if an event version is upgraded inside a projection or a new event added.

thoughts:

• should this only be for events? Or can we do commands too?
• what happens if a command is updated but only 1 handler is updated to use the new version?
• should handler projection names include a hash of handled event versions to prevent a user from updating the handler and not incrementing version?
• should we support event upgrading/downgrading into a specific handler?

[charlessolar]

After a chat - the way I was thinking about splitting was wrong.

We’d not be splitting on the event’s Versioned namespace - we’d be splitting based on the Handler namespace.

And a rule would be to not change other handler’s models (good practice in any case)

A model would be a self-contained unit inside a handler - and a projection would encompass all the events the 1 handler handles.

We can add a special Handler.Rebuilding hook method to allow the user to delete all the models they’ve built before starting the rebuild

[charlessolar]

Upon startup the endpoint would map out which events are handled by which handlers and create a single projection which links events to one of multiple handlers like so

'CustomerCreated': function(event, state) {
   linkTo('CustomerDetailsHandler.0.1');
   linkTo('CustomerAnalyticsHandler.0.1');
}

Specific details on versioning the handler streams and the projection itself will need to be thought about more deeply