Enhancement: Expected version for Event Store

[danielcirket]

We should allow for the equivalent of

ExpectedVersion.Any and ExpectedVersion.NoStream.

ExpectedVersion.Any

• If the events do not exist in the steam then should succeed
• If the events already exist in the stream then we should no-op or fail - requires more thought.
• If a partial number of the events exist in the stream we should fail.

ExpectedVersion.NoStream

• If the stream already exists, then we should fail.

Considerations

• Conflicts with potentially adding a unique constraint on stream id and version: https://github.com/danielcirket/OpenEventSourcing/issues/44
  • By default how should conflicts be handled, or how should the conflict be propagated? It might be the case that there isn't really a conflict so should be able to re-run the action against the latest version , however there may be cases where one or more events does conflict and will need resolving, do we want to provide any kind of building block(s) for this or leave it as an exercise to the consumer based on their requirements?