eventsourcing-java-example | Event Sourcing implementation for banking domain | Architecture library

This questions is about a very low level view of Event sourcing and depends a lot on the actual implementation of an Event store. All-in-all, I can give you an answer, hoping to shed some light on your understanding of Event stores.

Is the sole purpose of event stream to give ability to iterate over list of events that does not sound so useful maybe I am missing something but why can't I just get rid of event stream and call it a day?

Yes, an Event stream provides a mean to iterate over a possible large list of events, without retrieving all of them from the Event store in a blocking way. In general it is used only to read events, so its interface does not contain methods to append events to the Event store.

So, the client code needs only the events from the stream.

When adding events to an Event store, in order to protect from concurrent writes, one needs to pass the expected version of the Event stream. One can do this by using a version parameter to the method EventStore.appendEvents(expectedVersion, newEvents) or it can pass the previously loaded event stream and let the Event store retrieve the last seen version, thus reducing the coupling of the client code to the actual implementation of event stream locking mechanism. So, the signature of the appending method could be like this: